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Applied Catalysis A, General (v.443-444, #)
Exploration of acid–base geometric influence on cooperative activation for aldol reaction by Bo Liu; Heng Liu; Chunhua Wang; Lulu Liu; Shujie Wu; Jingqi Guan; Qiubin Kan (pp. 1-7).
Display Omitted► Organized acid–base bifunctionalized material. ► Effective radius for acid–base cooperativity. ► Influence of acid–base geometry on cooperativity.Bifunctionalized material with organized pairs of carboxylic acid and primary amine structurally similar to β3-amino acid derivatives has been prepared through post-grafted approach. Then the organized acid–base bifunctionalized material and the base monofunctionalized material were used as catalysts in aldol reaction to study the influence of the acid–base geometry on acid–base cooperativity. The catalytic result using acid–base bifunctionalized material towards aldol reaction was almost as same as the result obtained with the monofunctional amino catalyst, indicating that cooperative activation is not able to act efficiently unless the acid and the base active centers are positioned with appropriate geometry for the aldol reaction (e.g. about 2.6Å).
Keywords: Bifunctional materials; Acid–base geometry; Acid–base cooperativity; Mesoporous materials
Nanocatalysts for conversion of natural gas to liquid fuels and petrochemical feedstocks by Mahtab Gharibi; Farnaz Tahriri Zangeneh; Fereydoon Yaripour; Saeed Sahebdelfar (pp. 8-26).
Display Omitted► The conversion of natural gas by nanocatalysts is an active research field. ► Novel supports such as mesoporous solids have been widely used. ► Most achievements were in indirect conversions such as Fischer–Tropsch synthesis. ► Effective methane activation needs further theoretical and practical research.The conversion of natural gas (methane) as an alternative to petroleum into valuable chemicals and clean fuels has received much attention. However, because of high stability and symmetry of methane molecule, relatively few number of natural gas conversions, mostly indirect routes, have been commercialized and the remainders are still not competitive to petroleum-based processes and are in research and development stage. With the advent of nanocatalysts in chemical processes and energy sector, the potentials of these catalysts in natural gas conversions have been studied extensively all around the world. In indirect conversions, especially gas-to-liquid (GTL) technologies, effective nanocatalysts have been developed. However, in direct conversions, further research and development works are necessary. In this work, the advances in application of nanocatalysts in natural gas conversions are reviewed and areas for further research are addressed. Both theoretical aspects such as density functional theory (DFT) and characterizations and practical achievements in scientific and patent literature will be considered.
Keywords: Natural gas conversions; C; 1; chemistry; Liquid fuels; Nanocatalysts; Computational methods
Baeyer–Villiger oxidation of ketones catalysed by rhenium complexes bearing N- or oxo-ligands by Elisabete C.B.A. Alegria; Luísa M.D.R.S. Martins; Marina V. Kirillova; Armando J.L. Pombeiro (pp. 27-32).
Display Omitted► Re complexes catalyse the BV oxidation of cyclic and linear ketones with good conversions. ► Re catalysts are more active for the oxidation of cyclic than acyclic ketones. ► The highest activity occurs in 1,2-dichloroethane. ► The most active Re catalysts can operate in water as the only solvent.Rhenium (I, III–V or VII) complexes bearing N-donor or oxo-ligands catalyse the Baeyer–Villiger oxidation of cyclic and linear ketones ( e.g. 2-methylcyclohexanone, 2-methylcyclopentanone, cyclohexanone, cyclopentanone, cyclobutanone and 3,3-dimethyl-2-butanone) into the corresponding lactones or esters, in the presence of aqueous H2O2 (30%). The effects of various reaction parameters are studied allowing to achieve yields up to 54%.
Keywords: Baeyer–Villiger oxidation; Hydrogen peroxide; Rhenium complexes; Homogeneous catalysis; Ketones; Lactones; C-scorpionates; Pyrazole
Acidic characterization and activity of (NH4) xCs2.5− xH0.5PW12O40 catalysts in the esterification reaction of oleic acid with ethanol by Joicy S. Santos; José A. Dias; Sílvia C.L. Dias; Julio L. de Macedo; Fillipe A.C. Garcia; Liana S. Almeida; Eduardo N.C.B. de Carvalho (pp. 33-39).
Display Omitted► The mixed salts are much more stable than the parent acid (H3PW12O40). ► The FTIR of adsorbed pyridine displayed only Brønsted acidic sites. ► TG measurements indicated the formation of Py–H+⋯Py adducts. ► The best catalyst for esterification of oleic acid with ethanol was (NH4)2Cs0.5H0.5PW12O40. ► Good reutilization and no leaching were observed for (NH4)2Cs0.5H0.5PW12O40 catalyst.Ammonium and cesium derivatives from H3PW12O40 (H3PW), namely (NH4) xCs2.5− xH0.5PW12O40 ( x=0.5, 1, 1.5, 2), were synthesized and structurally characterized by FT-Raman spectroscopy, and their thermal stability was evaluated by FTIR and TGA/DTA. The acidity was characterized by the adsorption/desorption of gaseous pyridine, by FTIR and TGA/DTA as well as by the reaction of oleic acid and ethanol. The stability of the mixed salts regarding the Keggin structure was much higher than the parent acid, with the onset decomposition around 520°C. Nonetheless, calcination up to 300°C is recommended for the integrity of the mixed salt. The FTIR of adsorbed pyridine displayed only Brønsted acidic sites, which was confirmed by TGA measurements of the formation of Py–H+⋯Py adducts. The best esterification result was for (NH4)2Cs0.5H0.5PW12O40 with TOF=1.314molEOmol−1protons−1 with a 1:6 (oleic acid:ethanol) molar ratio, at 80°C and 10wt% catalyst in relation to the acid.
Keywords: Acidity; Heteropoly salts of cesium and ammonium; Thermal stability; Gas phase pyridine adsorption; 12-Tungstophosphoric acid; Nanostructured catalyst; Esterification; Oleic acid; Ethanol
Total oxidation of model volatile organic compounds over some commercial catalysts by Lenka Matějová; Pavel Topka; Květuše Jirátová; Olga Šolcová (pp. 40-49).
Display Omitted► Three commercial catalysts tested in total oxidation of VOCs at lab scale. ► Cu–Mn/alumina the most active and selective in oxidation of ethanol. ► Pt–Pd/alumina the most suitable for toluene oxidation. ► Pt–Pd/alumina–ceria the most active in dichloromethane oxidation. ► The highest HCl yield achieved with Pt–Pd/alumina.Commercial VOC oxidation catalysts can be used as comparative materials during development of new or improved catalysts. The objective of this study was to investigate physicochemical properties of EnviCat® commercial catalysts and their performance in total oxidation of three model compounds (dichloromethane, toluene and ethanol) at laboratory scale. The reactivity of model VOC was decreasing in the order ethanol>toluene>dichloromethane. The Cu–Mn/Al catalyst was found to be the most active and selective catalyst in ethanol oxidation. In oxidation of dichloromethane, the Pt–Pd/Al–Ce catalyst with 0.10wt% Pt+Pd was the most active, while the most selective one (giving the highest HCl yield) was the Pt–Pd/Al catalyst containing 0.24wt% Pt+Pd. In toluene oxidation, the Pt–Pd/Al catalyst with 0.24wt% Pt+Pd possessed the highest activity; the selectivity to CO2 was 100% for all investigated catalysts. Obtained results showed that the performance of commercial catalysts in laboratory scale tests can be different from that declared by catalyst supplier. A possible difference in catalytic performance at industrial and laboratory scale should be taken into account when industrial catalysts are used in laboratory scale tests.
Keywords: Oxidation; Volatile organic compounds; Ethanol; Toluene; Dichloromethane
The interaction mechanism of CO2 with CH3 and H on Cu (111) surface in synthesis of acetic acid from CH4/CO2: A DFT study by Riguang Zhang; Luzhi Song; Hongyan Liu; Baojun Wang (pp. 50-58).
.Display Omitted► The interaction mechanisms of CO2 with CH3 and H on Cu(111) surface are studied. ► All products are formed via the Eley–Rideal mechanism with gaseous CO2. ► CH3COO is preferably formed both kinetically and thermodynamically. ► HCOO is a primary side product. ► CH3OCO formation is not supported both kinetically and thermodynamically.The interaction mechanisms of CO2 with CH3 and H on Cu(111) surface in synthesis of acetic acid from CH4/CO2 are systematically investigated by the first-principle DFT–GGA calculations. Four possible reaction pathways are proposed, and the detailed mechanisms and kinetics are discussed. Our results show that all products are formed by gaseous CO2 and adsorbed CH3 and H through the Eley–Rideal (E–R) mechanism. It is found that the values of the activation barrier for four different pathways are in the order of CH3COO-Cu3OCO-Cu, suggesting that CO2 insertion into CuCH3 bond to form CH3COO-Cu is the most advantageous in dynamics among all four reaction pathways, and the corresponding activation barrier of the rate-controlled step is 85.2kJmol−1. The insertion of CO2 into CuH bond to form HCOO-Cu is secondly preferential pathway favored in dynamics. Therefore, H3CCOO is the main product, HCOO is a primary side product, and H3COCO are not obtained as it is inhibited by dynamics in comparison with other pathways. Above calculated results are in accordance with the experimental results, which can provide a new theoretical guidance for the direct synthesis of oxygenated compounds from CH4 and CO2.
Keywords: Carbon dioxide; Acetic acid; Hydrogen; Methyl; Density functional theory
The roles of Ce yZr1− yO2 in propane dehydrogenation: Enhancing catalytic stability and decreasing coke combustion temperature by Bao Khanh Vu; Eun Woo Shin; Jeong-Myeong Ha; Seok Ki Kim; Dong Jin Suh; Won-Il Kim; Hyoung-Lim Koh; Young Gyo Choi; Seung-Bum Lee (pp. 59-66).
Display Omitted► The role of Ce yZr1− yO2 in Pt-Sn/ xCeZr-Al was investigated in propane dehydrogenation. ► The presence of Ce yZr1− yO2 was crucial for ensuring catalytic stability. ► The presence of Ce yZr1− yO2 was crucial for a low regeneration temperature. ► The regeneration temperatures could be tailored by varying the Ce yZr1− yO2 content.The influence of Ce yZr1− yO2 content (0< y<1) in Pt-Sn/ xCeZr-Al catalysts, where x was the weight percentage of (Ce+Zr) and calculated as [mass of (Ce+Zr)]×100/[mass of (Ce+Zr+Al2O3)], on stability and regeneration temperature in propane dehydrogenation was studied using a fixed-bed reactor at 600°C and 1bar of pressure. The XRD data revealed that Ce yZr1− yO2 phases were formed over xCeZr-Al ( x≠0) supports and the concentration of Zr4+ ions in these phases increased when the Ce yZr1− yO2 content was increased. The band of oxygen vacancies characterized by Raman spectra at ca. 620–645cm−1 was strongly dependent on catalyst processing; introduction of metal (Pt, Sn) and/or re-calcination created more oxygen vacancies in the catalysts. The XRD patterns and XPS data of the reduced Pt-Sn/ xCeZr-Al catalysts did not indicate the formation of Pt-Sn alloys. The XPS and CO-IR spectra demonstrated that Pt became more electron deficient with increasing Ce yZr1− yO2 content. The higher catalytic stability and lower coke combustion temperature (regeneration temperature) were obtained with a higher Ce yZr1− yO2 content in Pt-Sn/ xCeZr-Al catalysts.
Keywords: Dehydrogenation; Ceria zirconia; Deactivation; Coke combustion
Fluid phase equilibria of the reaction mixture during the selective hydrogenation of 2-butenal in dense carbon dioxide by Nikolai E. Musko; Anker Degn Jensen; Alfons Baiker; Georgios M. Kontogeorgis; Jan-Dierk Grunwaldt (pp. 67-75).
Display Omitted► Pd-catalysed hydrogenation of 2-butenal to butanal in CO2. ► Bubble point pressures for the 2-butenal–CO2 binary were measured. ► Pure fluid and binary interaction parameters of the CPA EoS were estimated. ► Using CPA the number and composition of phases during the reaction were predicted. ► Highest catalytic conversion at the transition from two phases to a single phase.Knowledge of the phase behaviour and composition is of paramount importance for understanding multiphase reactions. We have investigated the effect of the phase behaviour in the palladium-catalysed selective hydrogenation of 2-butenal to saturated butanal in dense carbon dioxide. The reactions were performed using a 5wt% Pd on activated carbon in custom-designed high pressure autoclaves at 323K. The Cubic-Plus-Association (CPA) equation of state was employed to model the phase behaviour of the experimentally studied systems. CPA binary interaction parameters were estimated based on the experimental vapour–liquid or liquid–liquid equilibria data available in the literature. No experimental data for the CO2–2-butenal binary system were available in the literature; therefore, the bubble points of this mixture of varying composition at three different temperatures were measured in a high-pressure view cell. The results of the catalytic experiments showed that small amounts of carbon dioxide added to the system significantly decrease the conversion, whereas at higher loadings of CO2 the reaction rate gradually increases reaching a maximum. The CPA calculations revealed that this maximum is achieved in the so-called “expanded liquid” region, which is located near the critical point of the reacting mixture. It was also found that in this point the hydrogen concentration achieved its maximum in the CO2-expanded phase. Furthermore, the pressure – temperature regions where the multicomponent reaction system exists in one single phase and in multiphase were calculated.
Keywords: CO; 2; –2-butenal VLE; Supercritical CO; 2; Selective hydrogenation; Equations of state; CPA
Effect of Ti and Al addition via direct synthesis to SBA-15 as support for cobalt based Fischer-Tropsch catalysts by Matteo Lualdi; Gabriella Di Carlo; Sara Lögdberg; Sven Järås; Magali Boutonnet; Valeria La Parola; Leonarda Francesca Liotta; Gabriel M. Ingo; Anna Maria Venezia (pp. 76-86).
Display Omitted► SBA-15 supports doped with Al and Ti by direct synthesis kept hexagonal structure. ► The addition of titanium resulted in a decrease in channel length. ► All samples showed CO-diffusion limitations at low conversion level in FTS. ► Diffusion limitations were removed by a higher water partial pressure. ► Water addition increased the STY to HCs andSC5+ but enhanced the deactivation.Different mesoporous SBA-15 supports doped with Ti and Al at 5 and 10wt% have been synthesized by means of direct synthesis. The supports have been characterized by N2-adsorption, X-ray diffraction (XRD), temperature-programmed reduction (TPR), NH3-temperature programmed desorption (NH3-TPD), H2-chemisorption, X-ray photoelectron spectroscopy (XPS), field emission scanning electron microscope (FE-SEM), transmission electron microscopy (TEM). Titanium doped materials showed to have much shorter channels than the pristine SBA-15, while aluminum addition did not have a significant effect on channel length.After impregnation with 12wt% Co, the catalysts were further characterized and tested in the Fischer-Tropsch synthesis at industrially relevant process conditions (483K, 20bar, H2/CO ratio=2.1, pellet size: 53–90μm) with and without external water addition. TheSC5+ values of the different SBA-supported catalysts were low, especially at low conversion levels (i.e. low water partial pressure), suggesting that CO diffusion limitations increased the H2/CO ratio inside the 1-dimensional (1D) porous network.The selectivity data showed a correlation between the channel length and the extent of CO-diffusion limitations at much shorter diffusion distances than those for conventional 3D porous supports. Water partial pressure showed to increase the syngas diffusion rate (i.e. removal of diffusion limitations on reactants’ arrival), to have a positive kinetic effect on the rate and to favor longer chain hydrocarbons.
Keywords: Fischer-Tropsch; SBA-15; Doping; Diffusion limitations; Water
Iron-containing defect-rich mixed metal oxides for Friedel–Crafts alkylation by Benjamin Jäger; Antje Wermann; Peter Scholz; Matthias Müller; Udo Reislöhner; Achim Stolle; Bernd Ondruschka (pp. 87-95).
Display Omitted► Achieved TOFs for the CuFe2O4 and FeCr2O4 materials far exceed literature data. ► Combustion and mechano-chemical synthesis lead to much more defective materials. ► Synthesized materials are much more active allowing lower reaction temperatures. ► Also less activated arenes and secondary alkyl chlorides can be converted. ► Microstructural properties show major influence on the catalytic performance.Several stable iron-containing spinel oxides with the composition CuFe2O4 or FeCr2O4 were prepared by different methods including thermal nitrate decomposition, combustion synthesis, and mechano-chemical synthesis. Materials were compared to commercially available spinels produced by conventional ceramic route with respect to their structural properties and catalytic activity. Phase compositions and microstructures of the catalysts were studied in detail. The catalysts were tested in the Friedel–Crafts alkylation of various aromatic compounds with different alkyl halides as alkylating agents. Microstructural properties (microstrains) of the synthesized binary oxides have been identified as a reason for the increased reactivity. Even at low reaction temperatures of 50–70°C catalysts maintained their high activity resulting in TOFs of up to 3000h−1 and excellent selectivity with total heterogeneous behavior in catalysis.
Keywords: Combustion synthesis; Crystallite size; Friedel–Crafts alkylation; Liquid-phase catalysis; Mechano-chemical synthesis; Microstrains; Spinels
Enhanced photocatalytic activity of multi-doped TiO2 for the degradation of methyl orange by A. Charanpahari; S.S. Umare; S.P. Gokhale; V. Sudarsan; B. Sreedhar; R. Sasikala (pp. 96-102).
Display Omitted► Doping with multiple ions (Gd, N, S) enhances the photocatalytic activity of TiO2. ► In the multi-doped TiO2, S substituted for Ti whereas N substituted for O. ► Enhanced absorption of visible light is observed for multidoped-TiO2. ► Lifetime of the photogenerated charge carriers is higher in the doped samples.We report the synergistic effect of dopants like Gd, N and S in enhancing the photocatalytic activity of TiO2. Nanosized TiO2 doped at both cationic and anionic sites by Gd, N and S exhibited increased photocatalytic activity compared to TiO2 doped with either Gd or N and S. All the doped TiO2 existed as anatase phase and no separate phase due to Gd2O3 was seen up to a Gd concentration of 2%. The particle size as seen from the transmission electron micrograph was ∼25nm. The optical absorption property of TiO2 was improved by doping and redshift of the absorption edge is seen for all doped samples compared to pristine TiO2. The red shift of the absorption edge was the highest for the multiple ion-doped sample. Presence of bonded N and S in TiO2 was detected by X-ray photoelectron spectroscopy. Fluorescence lifetime studies indicated an enhanced lifetime for the charge carriers in the doped system compared to pristine TiO2. Photocatalytic activity study showed that the multi-doped sample has the highest activity for the degradation of methyl orange compared to Gd-TiO2, NS-TiO2 and pristine TiO2. The enhanced photocatalytic activity of the multi-doped TiO2 is attributed to factors such as improved optical absorption property and improved lifetime of the charge carriers.
Keywords: Gd N S doped TiO; 2; Photocatalyst; Photodegradation; Methyl orange; Fluorescence lifetime
Liquid-phase alkylation of benzene with ethylene over postsynthesized MCM-56 analogues by Bin Zhang; Yongjun Ji; Zhendong Wang; Yueming Liu; Hongmin Sun; Weimin Yang; Peng Wu (pp. 103-110).
Display Omitted► MCM-56 analogues were postsynthesized from MCM-22 precursors with various Si/Al ratios. ► MCM-56 analogues possess a partially delaminated structure consisting of disordered collection of MWW sheets. ► MCM-56 analogues are more active and durable than MCM-22 in the alkylation of benzene with ethylene.MCM-56 analogues were postsynthesized via a mild acid treatment technique from hydrothermally synthesized MCM-22 lamellar precursors with Si/Al ratios of 15–45. The physicochemical properties of MCM-56 were characterized by XRD, SEM, N2 adsorption, XPS,29Si and27Al MAS NMR, NH3-TPD and pyridine adsorption IR techniques. In comparison to MCM-22 with 3-dimensional MWW topology, the postsynthesized MCM-56 showed a broad X-ray diffraction of emerged 101 and 102 reflections and possessed a structural disorder along the layer stacking direction. Composed of partially delaminated MWW nanosheets, MCM-56 analogues had a larger external surface than MCM-22. The MCM-56 and MCM-22 catalysts were employed in the liquid-phase alkylation of benzene with ethylene. MCM-56 analogues exhibited a higher yield of ethylated benzenes and a higher catalytic stability than MCM-22, proving to serve as promising solid-acid catalysts for processing bulky molecules in petrochemical industry.
Keywords: MCM-56 analogue; MCM-22; Postsynthesis; Liquid-phase alkylation; Ethylbenzene
Metal vanadate catalysts for the ammoxidation of 2-methylpyrazine to 2-cyanopyrazine by Naresh Dhachapally; Venkata N. Kalevaru; Angelika Brückner; Andreas Martin (pp. 111-118).
Display Omitted► 2-Methylpyrazine to 2-cyanopyrazine ammoxidation was studied over metal vanadates. ► NbVO5 catalyst exhibits superior performance: yield 70%, conversion 100%. ► Surface vanadium to metal ratio plays a key role on the activity and selectivity. ► Formation of crystalline V2O5 revealed adverse effect on the catalytic performanceThe ammoxidation of 2-methylpyrazine to 2-cyanopyrazine was carried out in a fixed bed metal reactor in the temperature range of 320–460°C using a series of metal vanadate-containing solids (MV) as catalysts. These solids named as AlVO4, FeVO4, CrVO4, NbVO5, LaVO4 and BiVO4 were prepared with a nominal V/M ratio=1 always using the same synthesis procedure. Fresh and spent solids were characterized by X-ray diffraction, UV–vis DRS, XPS and pyridine-FTIR & ESR spectroscopy. The results revealed that the phase composition, near-surface-region behaviour and catalytic properties strongly depend on the nature of the metal used in MV solids. XRD showed the formation of crystalline MV phases in case of LaVO4 and BiVO4; whereas FeVO4 and CrVO4 exhibited poor crystallinity only. AlVO4 sample revealed the clear formation of crystalline V2O5 whereas in NbVO5 only a small proportion of V2O5 was detected. XPS depicted that the enrichment of vanadium in the near-surface-region is clearly dependent on the type of MV. It can be concluded that high near-surface-region V/M molar ratios promote the selectivity to cyanopyrazine but reduce the catalytic activity and vice versa. NbVO5 showed the best catalytic performance compared to all other MVs. Almost 69% yield of 2-cyanopyrazine at total conversion could be successfully obtained.
Keywords: Metal vanadates; Ammoxidation; 2-Methylpyrazine; 2-Cyanopyrazine; XRD; XPS; Pyridine-FTIR; ESR
Ammonia decomposition over Ni/La2O3 catalyst for on-site generation of hydrogen by Hiroki Muroyama; Chikara Saburi; Toshiaki Matsui; Koichi Eguchi (pp. 119-124).
Display Omitted► We prepared nickel catalysts supported on various metal oxides. ► We studied the activity of nickel catalysts for ammonia decomposition. ► The Ni/La2O3 catalyst exhibited relatively high activity. ► The extent of LaNiO3 formation was a key factor for catalytic activity of Ni/La2O3.Ammonia decomposition is a promising process for on-site generation of hydrogen. In this study, various nickel catalysts supported on metal oxides were prepared and their catalytic activity for ammonia decomposition was investigated. Ni/Al2O3 catalyst achieved the highest ammonia conversion among catalysts investigated due to the high surface area of Al2O3 support (200m2g−1). Despite the low surface area of support material (4.7m2g−1), the catalytic activity of Ni/La2O3 was comparable to that of Ni/Al2O3. The basicity of support materials was not specifically related with the catalytic activity. For Ni/La2O3 catalyst, the small nickel particles were deposited over La2O3 from LaNiO3 during the reduction treatment. When the Ni loading amount was changed in the range of 10–70wt% for Ni/La2O3 catalyst, the sample with 40wt% Ni exhibited the highest conversion of 78.9% at 550°C. The catalytic performance of Ni/La2O3 was also affected by the preparation method and calcination temperature. The LaNiO3 formation was responsible for the high activity of Ni/La2O3 catalyst for the ammonia decomposition.
Keywords: Ammonia decomposition; Nickel catalyst; Support effect; Lanthanum nickelate
Isomerization of α-pinene oxide catalyzed by iron-modified mesoporous silicates by Jakelyne V. Coelho; Augusto L.P. de Meireles; Kelly A. da Silva Rocha; Marcio C. Pereira; Luiz C.A. Oliveira; Elena V. Gusevskaya (pp. 125-132).
Display Omitted► Iron-modified mesoporous silicates were prepared by a direct hydrothermal method. ► The iron precursor nature (Fe2+ or Fe3+) strongly affected the material properties. ► The materials catalyze the liquid-phase isomerization of α-pinene oxide. ► The product distribution is remarkably dependent on the solvent nature. ► In acetone, the reactions gave highly valuable trans-sobrerol as a major product.Iron-modified mesoporous silicates (Fe-MCM) were prepared through a direct hydrothermal method and characterized by N2 adsorption–desorption, XRD, Mössbauer spectroscopy and SEM-EDS techniques. The nature of the iron precursor (Fe2+ or Fe3+) strongly affected the textural and morphological properties of the materials. Fe2+-MCM presented the morphology similar to sheets with nanometer dimensions, while Fe3+-MCM was more similar to the non-modified MCM. Characterizations suggest that most of the introduced iron species present on the material surface rather than in the silicate framework. Besides the framework included Fe3+ ions (0.2–0.3wt.%), both materials contain only the trivalent iron (as hematite). Hematite nanoparticles are highly dispersed on the Fe3+-MCM surface, whereas in Fe2+-MCM, hematite forms particles of both low and high dispersion. The materials were shown to be efficient heterogeneous catalysts for the transformation of α-pinene oxide in various value-added fragrance compounds, with the product distribution being remarkably dependent on the solvent nature.
Keywords: Iron catalysts; Isomerization; Mesoporous silicates; α-Pinene oxide
Sulfonic groups functionalized preoxidated polyacrylonitrile nanofibers and its catalytic applications by Linjun Shao; Guiying Xing; Luyao He; Ji Chen; Hangqing Xie; Xuezheng Liang; Chenze Qi (pp. 133-137).
Display Omitted► Nanoporous preoxidated polyacrylonitrile nanofiber mat was prepared by electrospinning and preoxidation. ► The preoxidated nanofiber mat was used to immobilize sulfonic groups via sulfonation. ► The morphologies of the nanofiber mats were examined by SEM images. ► The catalytic activities and reuse of the novel catalyst were examined for acetalization and esterification. ► The fiber structure could facilitate the recover and reuse of the solid acid catalyst.A SO3H-bearing nanofiber mat was synthesized and investigated as a novel heterogeneous acid catalyst. Preoxidated polyacrylonitrile nanofiber mat was prepared via electrospinning and heat treatment, and then reacted with chlorosulfuric acid to introduce the sulfonic groups. The nanofiber mat owned high acidity of 2.99mmol/g. The preoxidation and sulfonation were examined by FT-IR spectroscopy, elemental analysis and X-ray diffraction spectroscopy (XRD). The fiber morphologies were characterized by scanning electron microscopy (SEM). The catalytic activities and reuse of the prepared nanofiber mat solid acid catalyst have been evaluated for the acetalization and esterification. The regular fiber mat structure could significantly facilitate the recovery and reuse of the catalyst. The excellent catalytic performance and easy recycling made the novel fiber mat solid acid hold great potential for the green chemical processes.
Keywords: Solid acid; Preoxidation; Electrospun; Nanofiber
Ball-milling combined calcination synthesis of MoS2/CdS photocatalysts for high photocatalytic H2 evolution activity under visible light irradiation by Guoping Chen; Dongmei Li; Fan Li; Yuzun Fan; Haofei Zhao; Yanhong Luo; Richeng Yu; Qingbo Meng (pp. 138-144).
Display Omitted► A simple and effective ball-milling combined calcination method was developed. ► Molar ratio of MoS2 to CdS, ball-milling and calcination time were optimized. ► The highest H2 evolution rate was 1315μmolh−1 for the 0.9mol% MoS2/CdS (PT). ► The as prepared photocatalyst exhibits good anti-photocorrosion property.A simple and effective ball-milling combined calcination method has been developed to prepare MoS2/CdS photocatalysts for visible-light-driven water splitting into H2 for the first time. The photocataysts exhibit very high photocatalytic activities. A H2 evolution rate up to 1315μmolh−1 has been achieved based on 0.9mol% MoS2/CdS (PT) photocatalyst (PT is the abbreviation of pretreatment), which is much higher than 488μmolh−1 for the 0.2wt% Pt/CdS (PT) photocatalyst. In the meantime, this photocatalyst exhibits good anti-photocorrosion property. The ball-milling procedure makes the starting material, (NH4)2MoS4, disperse uniformly on the surface of CdS nanoparticles. Further calcination treatment leads to complete decomposition of (NH4)2MoS4 to afford MoS2/CdS photocatalysts with intimate contacts between the two components. The pretreatment of CdS also has important positive effect on photocatalytic activity. Similar reactions by attempting different kinds of commercial CdS products have been carried out, indicating this preparation method is universal.
Keywords: MoS; 2; /CdS; Ball-milling; Photocatalyst; H; 2; evolution; Visible light irradiation
Characterization of HNbMoO6, HNbWO6 and HTiNbO5 as solid acids and their catalytic properties for esterification reaction by J. He; Q.J. Li; Y. Tang; P. Yang; A. Li; R. Li; H.Z. Li (pp. 145-152).
Display Omitted► The acid strength was significantly affected by the state of protons. ► The acid strength follows the order HNbMoO6·H2O>HNbWO6·1.5H2O>HTiNbO5. ► HNbMoO6·H2O has the best catalytic activity for the esterification reaction. ► The catalytic activity for the esterification was mainly affected by gallery height.HTiNbO5, HNbMoO6·H2O and HNbWO6·1.5H2O were prepared by proton-exchange of the precursors KTiNbO5, LiNbMoO6 and LiNbWO6, respectively, which were synthesized by a solid-state reaction method. The morphology and the micro-structure were characterized by means of scanning electron microscope (SEM), transmission electron microscope (TEM), powder X-ray diffraction (XRD) and Fourier-transform infrared spectroscopy (FT-IR). NH3 temperature-programmed desorption (NH3-TPD) was used to measure the acidic properties of the samples. The Sanderson electronegativity and Kataoka′s bond strength theory were also applied to investigate the acid properties of the as-prepared samples. Finally, their catalytic activities were evaluated through catalyzing the liquid-phase esterification reaction of acetic acid and n-butanol to form n-butyl acetate. It has been revealed that H+ ions existed in different forms and interaction modes with MO bond in the solid acids. The acid strength for these as-prepared samples follows the order HNbMoO6·H2O>HNbWO6·1.5H2O>HTiNbO5. In this work, HNbMoO6·H2O presents an excellent catalytic activity for the esterification reaction, while HNbWO6·1.5H2O and HTiNbO5 have little catalytic activity. The result suggested that the catalytic activity of the layered solid acid for the esterification reaction was mainly controlled by gallery height.
Keywords: Titanoniobate; Niobium molybdate; Niobium tungstate; Acidic characteristics; Esterification reaction
V- or Mo-modified niobium catalysts for glycerin conversion reactions in the presence of H2O2 by Juber P. Souza; Thaís Melo; Marcone A.L. de Oliveira; Roberto M. Paniago; Patterson P. de Souza; Luiz C.A. Oliveira (pp. 153-160).
Display Omitted► V-doped niobia highly active was obtained by the generation of peroxo groups after treatment with H2O2. ► The mass spectrometry showed that ether was mainly produced. ► The catalytic activity of modified niobia was monitored under several conditions.In the present work, amorphous niobium oxides with 5% (w/w) vanadium or molybdenum isomorphically substituted into the material structure were synthesized. The materials were characterized by X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy (SEM/EDS), transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy (XPS). The results show that vanadium and molybdenum were incorporated into the niobium oxide structure with concomitant changes in the morphologic and catalytic properties. Catalytic studies on the conversion of residual glycerin generated during biodiesel production in the presence of H2O2 showed enhanced efficiency of ether formation with the vanadium-containing material. The NbV/ethanol/glycerin/250°C system was found to convert 80% of glycerin. Experiment-planning studies in conjunction with the analysis of the surface response via gas chromatography–mass spectrometry (GC–MS) aided in the determination of the optimal conditions. The catalytic tests monitored by GC–MS showed the formation a mixture of ethers obtained by the condensation of glycerol. Furthermore, it was observed that the modification of the catalyst directs the formation of larger molecules such as ketone mainly in the catalyst containing vanadium.
Keywords: Doped niobia; Glycerol conversion; Heterogeneous catalysis; Oxidation process
CO oxidation and preferential oxidation of CO in the presence of hydrogen over SBA-15-templated CuO-Co3O4 catalysts by S. Varghese; M.G. Cutrufello; E. Rombi; C. Cannas; R. Monaci; I. Ferino (pp. 161-170).
.Display Omitted► SBA-15-templated, rod-shaped Co3O4 and Co–Cu spinels were prepared. ► Cu is beneficial in the CO oxidation only at reaction temperatures above 100°C. ► PROX occurs with higher O2 and CO conversions on the Cu-containing catalysts. ► Cu enhances H2 combustion and, at high temperature, induces some methanation. ► Methanation seems catalyzed by metallic cobalt formed during the PROX run.Copper–cobalt mesostructured spinel replicas of SBA-15 were synthesized through a hard template pathway. The catalysts, with Cu/(Co+Cu) atomic ratio in the range 0–17%, were characterized as to their structure, morphology, texture and redox features by X-ray diffraction, FTIR spectroscopy, transmission electron microscopy, N2 physisorption, and temperature-programmed reduction with hydrogen. The catalysts were tested in a fixed-bed reactor for CO oxidation both in the absence of hydrogen (1.5mol% CO, 1.5mol% O2, balance He, 40–140°C) and in a hydrogen-rich atmosphere (1.5mol% CO, 1.5mol% O2, 46mol% H2, balance He, 40–200°C). In the absence of hydrogen, catalytic activity for CO oxidation was similar for all the samples for temperatures up to ca. 100°C, at which 50% CO conversion was observed. Above such temperature the copper-containing catalysts appeared more active than the pure Co3O4. All the catalysts were active for the preferential oxidation of CO in hydrogen-rich atmosphere, with 50% CO conversion occurring in the 123–138°C range. Both CO and oxygen conversions were enhanced by the presence of copper, which however also favoured the occurrence of parasite hydrogen combustion. Methanation was observed (to a limited extent, at temperatures ≥160–180°C) only on the Cu-containing catalysts. The performance of the present catalysts was compared with literature results for CO oxidation and preferential CO oxidation on cobalt and copper–cobalt oxides prepared by different methods. The hard-templated catalysts seem superior to traditionally prepared ones in the case of CO oxidation in the absence of hydrogen, whereas no clear-cut conclusion can be drawn in the case of preferential CO oxidation.
Keywords: Hard template (HT); Cobalt oxide; Copper oxide; CO oxidation; CO PROX
Ethanol transformation into hydrocarbons on ZSM-5 zeolites: Influence of Si/Al ratio on catalytic performances and deactivation rate. Study of the radical species role by Filipa Ferreira Madeira; Karima Ben Tayeb; Ludovic Pinard; Hervé Vezin; Sylvie Maury; Nicolas Cadran (pp. 171-180).
Display Omitted► Ethanol transformation is accompanied by a great loss of acidity and microporosity. ► The Brønsted acid sites and the radicals are active sites for ethanol conversion. ► An optimum balance between both is required for obtaining a high yield in hydrocarbons. ► HZSM-5(40) was found to be the most stably and selective catalyst toward hydrocarbons yield. ► A change of radical species nature with TOS is responsible for the deactivation.The catalytic performances of HZSM-5 zeolites with Si/Al ratios ranging from 16 to 500 were investigated for ethanol transformation into hydrocarbons. The fresh and used catalysts were characterized by a combination of nitrogen adsorption, pyridine adsorption followed by infrared spectroscopy (IR), gas chromatography–mass spectrometry (GC–MS) coupling and electron paramagnetic resonance (EPR). HZSM-5(Si/Al=40) was found to be the most stably and selective catalyst due to an optimum balance between the number of Brønsted acid sites and the amount of radicals, which are active sites for ethanol conversion into higher hydrocarbons. However, a change of radical species nature occurred with time-on-stream (TOS) which could be responsible for the deactivation of all catalysts leading to a decrease of C3+ hydrocarbons yield.
Keywords: Brønsted acidity; Coke composition; Radical; Deactivation; Ethanol conversion
Synthesis of gel-type imino-amino functionalized methacrylate-styrene terpolymers as supports for palladium catalysts for the Suzuki–Miyaura reaction by Karol Bester; Agnieszka Bukowska; Wiktor Bukowski (pp. 181-190).
Display Omitted► Novel recyclable Pd catalysts for Suzuki–Miyaura reaction under mild conditions. ► Imino-amino functionalized methacrylate-styrene gels as supports for Pd catalysts. ► Pd(II) ion loading as a factor in determining the activity of polymer catalysts. ► An advantageous effect of branching ligand systems on the activity of Pd catalysts.Gel-type polymers uploaded with 8.5–15.4wt% of palladium(II) ions based on the low cross-linked glycidyl methacrylate resins with imino-amino functionalities coupled with heterocyclic rings were prepared, characterized (FT-IR, DR UV–vis, HR-SEM, ICP-OES methods) and tested as catalysts in the Suzuki–Miyaura reactions of a series bromo- and chloroarenes with phenylboronic acid at 25–70°C. The effects of the reaction medium, temperature, catalyst structure and concentration on the activity of the catalysts and Pd leaching were studied for the model reaction of bromobenzene with phenyl boronic acids. It was found that the catalysts with the branched system of TAEA were more active than those with the linear one (EDA). The activity of the catalysts strongly depended on the nature of heteroatoms of heterocyclic aldehyde moieties in imine ligands. The catalyst activity decreased in the order: 2-pyridinecarboxaldehyde (PA)>furfural (FA)>2-thiophenecarboxaldehyde (TA). The best of the catalysts was used additionally in the reactions of substituted bromo- and chloroarenes. It turned out to catalyze efficiently the cross-coupling of bromoarenes bearing both electron donor and electron acceptor substituents. The reactivity of bromoarenes changed in the order: CHO>H∼F>Me>OMe≫OH. The catalyst was found inactive in coupling of 4-nitrochlorobenzene under the same reaction conditions. The catalyst with TAEA moieties was recycled in the reaction of bromobenzene minimum five times. Its activity, however, decreased gradually on each stage.
Keywords: Polymer supported palladium catalyst; Gel-type polymer supports; Imino-amino functionalized polymers; Suzuki–Miyaura reactions
Modification of the supported Cu/SiO2 catalyst by alkaline earth metals in the selective conversion of 1,4-butanediol to γ-butyrolactone by Bin Zhang; Yulei Zhu; Guoqiang Ding; Hongyan Zheng; Yongwang Li (pp. 191-201).
.Display Omitted► The promotion effects of alkaline earth metals over the Cu/SiO2 catalyst were studied. ► Cu-Ba/SiO2 exhibited the best performance in 1,4-butanediol dehydrogenation. ► The interaction of the promoter, copper and support were discussed. ► The γ-butyrolactone was generated over the copper surface. ► The byproduct 2,3-dihydrofuran was generated over the metal and acid–basic sites.The promotion effects of alkaline earth metals (Mg, Ca, Sr, Ba) on the catalytic property of the Cu/SiO2 catalyst for the gas phase dehydrogenation of 1,4-butanediol were investigated. The addition of Ca, Sr or Ba to the Cu/SiO2 catalyst resulted in the improvements of the catalytic activity and the γ-butyrolactone selectivity, and the Cu-Ba/SiO2 catalyst gave 99.6% yield of γ-butyrolactone even after 900h running. The catalysts were prepared by co-impregnation and characterized by N2 physisorption, X-ray diffraction (XRD), SEM, TEM, H2-temperature programmed reduction (H2-TPR), N2O-decomposition, ammonia temperature-programmed desorption (NH3-TPD), CO2-TPD, XPS, and FTIR spectroscopy of adsorbed pyridine and CO. On the base of the experimental results, two types of copper species on the reduced catalyst were proposed. The Cu° account for the dehydrogenation of 1,4-butanediol, while the electropositive copper species (Cu+) is suggested to be the strong Lewis acid site to catalyze side reactions. The selectivity of γ-butyrolactone was increased with the increasing of the Cu0/Cu+ ratio, and the yield of γ-butyrolactone was increased with copper surface area. The main byproduct 2,3-dihydrofuran may be formed from 1,4-butanediol by the metal/acid–base concerted catalysis.
Keywords: Alkaline earth metals modified Cu/SiO; 2; 1,4-Butanediol; γ-Butyrolactone; Dehydrogenation
Simultaneous conversion of triacylglycerides and fatty acids into fatty acid methyl esters using organometallic tin(IV) compounds as catalysts by Yariadner C. Brito; Daví A.C. Ferreira; Danielle M. de A. Fragoso; Paula R. Mendes; César M.J. de Oliveira; Mario R. Meneghetti; Simoni M.P. Meneghetti (pp. 202-206).
Display Omitted► All complexes based on Sn(IV) are active in esterification. ► BTA is able to convert simultaneously TAG and FFA in FAMEs with high yields. ► It is possible to convert oils with very high FFAs content into FAMEs.Three Sn(IV) complexes, named butyl stannoic acid (BTA), di- n-butyl-oxo-stannane (DBTO) and dibutyltin dilaurate (DBTDL), were initially tested as catalysts for esterification reaction of fatty acids in the presence of methanol as alcoholysis agent. Parameters like reaction time, temperature, and catalyst amount were systematically evaluated in this work. All complexes were active at relative high reaction temperatures, but BTA displayed the highest activity. Former studies have already demonstrated that these same complexes display good catalytic activity in methanolysis of triacylglycerides (TAGs). These results prompted us to test BTA catalyst also in simultaneous esterification/transesterification reactions from a mixture of free fatty acids (FFAs) and TAGs in the presence of methanol. BTA was able to convert the mixtures in to fatty acid methyl esters (FAMEs) with good yields, with simple isolation processes. The results obtained and discussed in this work can help the development of new catalytic systems to biodiesel production from oils with very high acid content.
Keywords: Transesterification; Esterification; Simultaneous transesterification and esterification; Biodiesel; Tin catalysts; Chemical computational studies
Tungstophosphoric acid/zirconia composites prepared by the sol–gel method: An efficient and recyclable green catalyst for the one-pot synthesis of 14-aryl-14 H-dibenzo[ a, j]xanthenes by Toa S. Rivera; Alexis Sosa; Gustavo P. Romanelli; Mirta N. Blanco; Luis R. Pizzio (pp. 207-213).
Display Omitted► Zirconia modified with tungstophosphoric acid samples were synthesized. ► The SBET decreases and the microporosity increases with the increase of TPA content. ► The species present in the samples are [PW12O40]3−, [P2W21O71]6− and [PW11O39]7− anion. ► Aryl-14 H-dibenzo[ a, j]xanthenes have been synthesized by a one-pot condensation. ► Condensation of 2-naphthol and aryl aldehydes catalyzed by TPA/zirconia composites.Samples of zirconia modified with different contents of tungstophosphoric acid (TPA) were synthesized from zirconium propoxide via sol–gel reactions using polyethylene glycol as template and were characterized by different physicochemical techniques (BET, XRD, FT-IR, and31P MAS-NMR). The SBET of the solids decreases and the microporosity increases with the increase of the TPA content. According to FT-IR and31P MAS-NMR studies, the main species present in the samples is [PW12O40]3− anion, which was partially transformed into [P2W21O71]6− and [PW11O39]7− anions during the synthesis and drying steps. The XRD patterns of the modified samples exhibit neither the characteristic peaks of TPA nor those attributed to its decomposition products.Aryl-14 H-dibenzo[ a, j]xanthenes have been synthesized by a one-pot condensation of 2-naphthol and aryl aldehydes, catalyzed by tungstophosphoric acid/zirconia composites in a solvent-free medium using conventional heating. The present approach offers the advantages of clean reaction, simple methodology, short reaction time, and high yield. The reaction work-up is very simple and the catalyst can be easily separated from the reaction mixture and reused several times in subsequent reactions without appreciable loss of the catalytic activity.
Keywords: Mesoporous zirconia; Heteropolyacids; 14-Aryl-14; H; -dibenzo[; a; ,; j; ]xanthenes; Heterogeneous catalysis; Solvent-free reaction
Side-chain alkylation of toluene with methanol to styrene over cesium ion-exchanged zeolite X modified with metal borates by Balkrishna B. Tope; Wahab O. Alabi; Abdullah M. Aitani; Hideshi Hattori; Sulaiman S. Al-Khattaf (pp. 214-220).
Display Omitted► Metal borate modified-Cs-X shows a high activity to form styrene from toluene and methanol. ► Among metal borates, zirconium borate is most effective. ► Mechanical mixing of Cs-X and metal borates followed by calcination produces good catalysts. ► Modification of Cs-X with metal borates facilitates the formation of formaldehyde from methanol.Cesium ion-exchanged zeolite X (Cs-X) was modified with metal borates to prepare efficient catalysts for side-chain alkylation of toluene with methanol to styrene. The catalytic behavior of Cs-X was improved by the modification with metal borates such as zirconium borate, zinc borate, copper borate and lanthanum borate. Modification was performed by mechanical mixing of Cs-X and a metal borate in dry state followed by calcination. Significant enhancement of activity was observed for modification with zirconium borate and zinc borate. The selectivity to styrene was increased by modification with all metal borates. Modification with metal component or boron alone was not so effective as that with metal borate. The highest activity was obtained with the Cs-X modified with 10wt% zirconium borate and calcined at 773K. The high activity of metal borate-modified Cs-X is due to the ability to selectively form formaldehyde from methanol, which is suggested by appearance of clear IR peak at 1690cm−1 assigned to unidentate formate species on adsorption of methanol. The basic sites and acidic sites of Cs-X were slightly weakened by modification with metal borates. It was revealed that mechanical mixing of Cs-X and metal borates followed by calcination is a good method to prepare Cs-X modified with both metal components and boron.
Keywords: Styrene; Toluene; Methanol; Side-chain alkylation; Metal borate-modified cesium ion-exchanged zeolite