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Applied Catalysis A, General (v.333, #2)
Nanosized gold catalysts supported on ceria and ceria-alumina for WGS reaction: Influence of the preparation method by D. Andreeva; I. Ivanov; L. Ilieva; J.W. Sobczak; G. Avdeev; T. Tabakova (pp. 153-160).
Gold supported catalysts on ceria-alumina, prepared by different methods have been studied in the WGS reaction. Gold catalysts on ceria-alumina, prepared by mechanochemical activation show a high and stable WGS activity. A correlation between redox and catalytic activity was observed. The introducing of alumina to ceria by mechanochemical activation causes formation of oxygen vacancies, located mainly on the catalyst surface. A positive effect of alumina on the catalysts stability was established.▪Gold supported catalysts on ceria-alumina, prepared by different methods have been studied in the WGS reaction. For the synthesis of the mixed ceria-alumina support two methods were applied—a new method of mechanochemical activation and well known ceria washcoating on alumina. Gold catalysts on ceria-alumina, prepared by mechanochemical activation show a high and stable WGS activity. A correlation between redox activity of the catalysts, estimated by TPR and the catalytic activity of the samples was observed. The introducing of alumina to ceria by mechanochemical activation causes formation of oxygen vacancies, located mainly on the catalyst surface. In the freshly prepared catalysts an optimum between a part of positively charged nano-gold particles, Ce3+ and oxygen vacancies should be the crucial factor for the good performance of WGS catalysts. In the course of redox reaction the active complex is being changed because of the electron transfer between gold and ceria through oxygen vacancies. A positive effect of alumina on the catalysts stability with respect to avoiding gold and ceria particles agglomeration was confirmed, as well.
Keywords: Nanosized gold and ceria; Ceria-alumina; Mechanochemical activation; WGS
Effect of the support on the kinetic and deactivation performance of Pt/support catalysts during coupled hydrogenation and ring-opening of pyrolysis gasoline by P. Castaño; A. Gutiérrez; B. Pawelec; J.L.G. Fierro; A.T. Aguayo; J.M. Arandes (pp. 161-171).
The upgrading of an aromatic-rich feedstock (pyrolysis gasoline) has been investigated over bifunctional Pt catalysts in order to evaluate the effect of the support on conversion, selectivity and deactivation. The experiments were conducted in a fixed-bed reactor at a pressure of 5MPa and 350–450°C. Pt was incorporated into five acidic supports: MFI, BEA and FAU zeolites, and an amorphous silica-alumina (ASA). Their surface properties and acidity were then assessed by means of several characterization techniques and related with their intrinsic activity–selectivity–deactivation. Using high hydrogen pressure (to minimize catalyst deactivation), we report the suitability of several catalysts for different purposes: Pt/MFI19 catalyst for a steam cracker feedstock production, Pt/BEA catalyst for isoalkane-rich gasoline pool manufacture and Pt/ASA catalyst for severe aromatic reduction while controlling the extent of ring scission. The results of accelerated deactivation experiments under low hydrogen pressure lead to the conclusion that MFI-supported catalysts (Pt/MFI19 and Pt/MFI95) yield less coke, but Pt/BEA deactivates to a lesser extent during hydrogenation.▪The upgrading of an aromatic-rich feedstock (pyrolysis gasoline) has been investigated over bifunctional Pt catalysts in order to evaluate the effect of the support on conversion, selectivity and deactivation. The experiments were conducted in a fixed-bed reactor at a pressure of 5MPa and 350–450°C. Pt was incorporated into five acidic supports: MFI, BEA and FAU zeolites, and an amorphous silica-alumina (ASA). Their surface properties and acidity were then assessed by means of several characterization techniques and related with their intrinsic activity–selectivity–deactivation. Using high hydrogen pressure (to minimize catalyst deactivation), we report the suitability of several catalysts for different purposes: Pt/MFI19 catalyst for a steam cracker feedstock production, Pt/BEA catalyst for isoalkane-rich gasoline pool manufacture and Pt/ASA catalyst for severe aromatic reduction while controlling the extent of ring scission. The results of accelerated deactivation experiments under low hydrogen pressure lead to the conclusion that MFI-supported catalysts (Pt/MFI19 and Pt/MFI95) yield less coke, but Pt/BEA deactivates to a lesser extent during hydrogenation.
Keywords: Hydrodearomatization; Ring-opening; Hydrotreatment; Pyrolysis gasoline; Platinum bifunctional catalysts; Zeolites HY; Hβ; HZSM-5; Amorphous silica alumina
Preparation of CuCl/1,10-phenanthroline immobilized on polystyrene and catalytic performance in oxidative carbonylation of methanol by Wanling Mo; Haitao Liu; Hui Xiong; Ming Li; Guangxing Li (pp. 172-176).
An immobilized catalyst CuCl/Phen-PS was synthesized, and the catalyst exhibited high catalytic activity, excellent stability in consecutive catalytic runs, easy separation from reaction mixture and low leaching of active metal species in oxidative carbonylation of methanol.▪The heterogenization of homogeneous catalysts combines the advantages of both heterogeneous and homogeneous catalysis systems. In oxidative carbonylation of methanol to dimethyl carbonate (DMC), a novel heterogenization of a homogeneous catalyst system, CuCl/1,10-phenanthroline immobilized on polystyrene, was investigated. Characterizations with FTIR, XPS, EA, TGA and AA revealed that CuCl was successfully immobilized on polystyrene modified 1,10-phenanthroline (Phen-PS) through chelating between the N– N bidentate ligand and Cu. The catalytic performance of the CuCl/Phen-PS catalyst tested proved that it is an efficient heterogenized catalyst for the oxidative carbonylation of methanol. The conversion of methanol, the selectivity to DMC and the yield of DMC based on O2 were 15.5%, 96.4% and 78.2%, respectively, at 120°C, 5h, 3.0MPa, andPCO:PO2=9:1. The CuCl/Phen-PS catalyst retains its catalytic activity after seven recycles. The average weight loss of CuCl/Phen-PS was about 2.2%, and the leaching of copper was about 0.68% in each recycle.
Keywords: Heterogenization of homogeneous catalyst; Oxidative carbonylation; Dimethyl carbonate; Phenanthroline; Polystyrene; Cuprous chloride
Fischer–Tropsch synthesis: Temperature programmed EXAFS/XANES investigation of the influence of support type, cobalt loading, and noble metal promoter addition to the reduction behavior of cobalt oxide particles by Gary Jacobs; Yaying Ji; Burtron H. Davis; Donald Cronauer; A. Jeremy Kropf; Christopher L. Marshall (pp. 177-191).
TPR-XANES/EXAFS carried out using a novel multi-sample holder provided key information for verifying the nature of the chemical transformations occurring during cobalt Fischer–Tropsch synthesis catalyst activation in hydrogen. In the past, assumptions had to be made regarding the nature of the cobalt species present along the trajectory of a standard TPR experiment. The new technique directly provided insight into (a) the nature of the reduction process of cobalt oxide species and (b) the resulting cobalt crystallite size, as a function of the strength of the catalyst support interaction with the cobalt oxide species. A two-step reduction process involving Co3O4 to CoO and CoO to Co0 transformations over standard calcined catalysts was observed and quantified over all catalysts exhibiting both weak interactions (e.g., Co/SiO2) and strong interactions (e.g., Co/Al2O3) with the support. Noble metal promoter (e.g., Pt) addition strongly improved the reducibility of cobalt oxide species, most likely via a H2 dissociation and spillover mechanism. Increasing cobalt loading, on the other hand, led to a measurable, but lesser, improvement on reducibility, due to the larger resulting particle size that resulted in less surface contact with the support. Higher reduction temperatures were needed to effectively reduce cobalt oxide particles deposited on strongly interacting surfaces in comparison with unsupported Co3O4 or only weakly interacting supported cobalt catalyst. Nevertheless, despite lower extents of reduction, the smaller resulting Co particles on the more strongly interacting catalysts generally led to higher Co0 active site densities. The addition of the noble metal promoter to strongly interacting supported catalyst significantly decreased the temperature required to reduce the cobalt oxides to Co0 particles; this allows one to take advantage of the higher Co0 surface areas arising from the combination of a smaller average Co0 particle size and a higher extent of reduction.Hydrogen TPR-XANES/EXAFS defined a two-step reduction process involving Co3O4 to CoO and CoO to Co0 transformations over calcined catalysts. These steps were quantified over catalysts exhibiting weak interactions (e.g., Co/SiO2) and strong interactions (e.g., Co/Al2O3) with the support. Noble metal promoter (e.g., Pt) addition improved the reducibility of both steps. ▪
Keywords: Fischer–Tropsch synthesis; Gas-to-liquids; Cobalt (Co); Cobalt oxide; (CoO, Co; 3; O; 4; ); Reduction; TPR; TPR-EXAFS; TPR-XANES; Multi-sample holder; Noble metal promoters; Platinum (Pt); Alumina (Al; 2; O; 3; ); Silica (SiO; 2; ); Metal support interaction
Low temperature water–gas shift: Applications of a modified SSITKA–DRIFTS method under conditions of H2 co-feeding over metal/ceria and related oxides by Gary Jacobs; Burtron H. Davis (pp. 192-201).
Three applications of a modified SSITKA–DRIFTS technique demonstrate the importance of designing catalysts for fuel processor applications in terms of a formate mechanism. Switching between12CO and13CO was carried out under steady state water–gas shift conditions with a feed containing co-fed H2. The dynamic responses of surface species and CO2 product were evaluated in terms of their times required to achieve 50% fractional isotopic exchange. In all cases studied, the formate ν(CH) band was observed to switch at a rate similar to the gas phase asymmetric ν(CO2) band. In the first application, the method was employed to monitor and corroborate the normal kinetic isotope effect that has been suggested to link the rate limiting step of water–gas shift to formate decomposition via C–H bond cleaving. Also observed was that when the ν(CO) band for adsorbed CO on Pt was completely exchanged, the ν(CO2) band had only achieved 50% exchange, casting doubt on the proposed mechanism involving the direct reaction of Pt–CO with O adatoms on ceria to produce gas phase CO2. In a second study, the impact of metal loading on the formate switching rate led to a remarkable decrease in the switching times of both formates and CO2 product, emphasizing the need to express the reaction pathway in terms of a bifunctional mechanism involving both the oxide, where formates are formed at Type II bridging OH groups, and the metal, where dehydrogenation of formate proceeds rapidly. The results suggest that when the loading of Pt was greater, a higher fraction of rapidly reacting formate close to the metal–ceria interface was present. In contrast, when the Pt loading was low, a considerable fraction of formate was located further from the metal and required time to diffuse to the metal–oxide interface prior to decomposition. Finally, a demonstration of the usefulness of the technique in determining whether an associative mechanism holds true for other partially reducible oxide components is provided. Oxides included ceria, thoria, zirconia, and a mixed ceria–zirconia oxide sample. Limitations of the modified SSITKA technique regarding experimentation and data interpretation are also considered.Three applications of the SSITKA–DRIFTS technique demonstrate the importance of considering a formate mechanism in water–gas shift catalyst design. Switching between12CO and13CO was carried out under steady state water–gas shift conditions with a feed containing co-fed H2. The method was used to probe the kinetic isotope effect, the impact of Pt loading, and the screening of partially reducible oxides.▪
Keywords: Steady state isotopic transient kinetic analysis (SSITKA); Diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS); Isotopic tracers; Isotopic switching; Type II bridging OH groups; Ceria (CeO; 2; ); Thoria (ThO; 2; ); Zirconia (ZrO; 2; ); Ceria–zirconia (CeO; 2; –ZrO; 2; ); Mixed oxide; Fuel processor; Water gas shift; Low temperature water gas shift (LTS); Hydrogen (H; 2; ); CO removal
Effect of La addition on catalytic performance of PtSnNa/ZSM-5 catalyst for propane dehydrogenation by Yiwei Zhang; Yuming Zhou; Hui Liu; Yu Wang; Yi Xu; Peicheng Wu (pp. 202-210).
The addition of La can have obvious influence on catalytic performance of PtSnNa/ZSM-5 catalyst for propane dehydrogenation. It is found that suitable content of La can improve the catalytic stability and selectivity to propene effectively. However, the opposite effect is observed when the loading of La is excessive. In order to discuss the possible reasons, the catalysts are characterized by several techniques and particular emphasis is focused on the changes of catalytic acidity and character of Pt active sites by the modification of La.▪PtSnNaLa/ZSM-5 catalysts with different amounts of lanthanum were prepared by sequential impregnation method, and characterized by XRD, nitrogen adsorption, NH3-TPD, FT-IR, TPR, H2-TPD, XPS and TPO techniques. It was found that the La species were well dispersed on the internal and external surfaces of ZSM-5 zeolite. With a little addition of La, the catalyst acidity decreased slightly and the active sites of the catalyst were stabilized, which resulted in the increased catalytic selectivity and stability. In PtSnNaLa/ZSM-5 catalyst containing 1.4% La, the stability of catalyst reached the best state and the catalytic selectivity was at the maximum. The average yield of propene was about 35.2% over 80h for the reaction of propane dehydrogenation at 590°C. However, as the La content increased, the character of Pt active sites changed obviously and the amount of Lewis acid sites increased, which in consequence decreased the catalytic activity and selectivity. Results from XPS analysis indicated that the addition of La could inhibit the reduction of tin species. Temperature-programmed oxidation (TPO) experiments showed that suitable loading of La could prevent the catalyst from coking effectively, whereas the opposite effect was observed when the content of La was excess.
Keywords: Lanthanum; ZSM-5; Pt–Sn catalyst; Propene; Propane dehydrogenation
Elucidation of reaction network and effective control of carbon number distribution in the three phase Fischer–Tropsch synthesis by Xiaohao Liu; Xiaohong Li; Yoshifumi Suehiro; Kaoru Fujimoto (pp. 211-218).
This article is to deal with the secondary reactions of 1-olefins during Fischer–Tropsch and to selectively synthesize the “FT” products in the desired range (middle distillates and wax) by controlling the pathway reaction shown in the Figure below. In this study, around 90% selectivity in middle distillates and heavy wax has been achieved in olefin-added FT synthesis. We have also experimentally evidenced the disproportionate reaction of 1-olefins in the presence of hydrogen only. ▪Reactions over olefins introduced during FT synthesis have been studied in a trickle bed reactor. Incorporation of 1-olefins into a growing alkyl chain could remarkably enhance the selectivity up to around 90% in heavy wax or middle distillate from syngas and could decrease the yields of lighter hydrocarbons with a higher CO conversion compared to the conventional FT synthesis. Results showed two significant processes the degradation of 1-olefins with successive demethylation, and its chain growth with incorporation by methylene species formed from demethylation, which is defined as the disproportionate reaction. The disproportionate reaction is competitive with introduced 1-olefins incorporating CH2 species formed from syngas into heavier hydrocarbons and is effectively controllable; Such control strongly depends on the process conditions. In general, the elimination of diffusion limitations for introduced 1-olefins and operating conditions that give a high intrinsic chain growth probability ( α value) are favorable for suppressing the disproportionate reaction and for promoting the chain growth by the incorporation of syngas-formed CH2 species to increase the yields of heavier FT products.
Keywords: Fischer–Tropsch synthesis; Co/SiO; 2; catalyst; Co-fed olefins; Disproportionate reaction; Chain initiation; Carbon number distribution
Hydrogenation of 2-ethyl-9,10-anthraquinone on Pd-polyaniline(SiO2) composite catalyst by Alicja Drelinkiewicz; Anna Waksmundzka-Góra; J.W. Sobczak; Jaroslav Stejskal (pp. 219-228).
The effect of humidity on the hydrogenation of 2-ethyl-9,10-anthraquinone (eAQ) was studied using Pd catalysts supported by silica coated with polyaniline (PANI) film. The film of polymer exhibits advantageous role observed as the exclusive transformation of hydroquinone form by phenyl ring saturation to give H4eAQH2 (active quinone) and strong suppression of eAQ degradation. This attractive reactivity is independent of the level of humidity in the reaction system. ▪The role of humidity in the hydrogenation of 2-ethyl-9,10-anthraquinone (eAQ) was studied using palladium catalysts supported on silica (SiO2) coated with polyaniline (PANI). Polymer was deposited on the support, SiO2, during “in situ” polymerization of aniline. Two series of catalysts (0.5wt.% Pd) differing in ordering of PANI macromolecules in the polymer film were used. The role of humidity was studied in the desired eAQ to eAQH2 (2-ethyl-9,10-anthrahydroquinone) reduction (quinone–hydroquinone stage), and in the consumption of primary and desirable product, eAQH2. The influence of humidity, especially in the course of hydroquinone form transformation, varied depending on the morphology of polymer film. At the high level of humidity a trend in the reactivity change of catalysts with thin and denser polymer film is similar to that for typical 0.5% Pd/SiO2 catalyst. On the other hand, reactivity of catalysts with “brush-like” ordering of PANI macromolecules does not change even at high level of humidity in the system. On these catalysts, the increase in humidity level has no influence on directing the consumption of eAQH2, and on the course of hydrogenolytic reactions producing 2-ethylanthrone (eAN). The hydroquinone form eAQH2 was exclusively transformed by phenyl ring saturation to give H4eAQH2 (active quinone, 2-ethyl-5,6,7,8-tetrahydro-9,10-anthrahydroquinone) with strong suppression of hydrogenolytic reactions yielding degradation products. This advantageous reactivity observed for all the PANI film-containing catalysts is related to the modification of environment surrounding of the Pd centres by the presence of hydrophobic polymer. Its role may be considered as the influence of polymer on the accessibility of reactants to the Pd centres and the geometry of reactant molecules adsorption.
Keywords: Abbreviations; eAQ; 2-ethyl-9,10-anthraquinone; eAQH; 2; 2-ethyl-9,10-anthrahydroquinone; H; 4; eAQ; 2-ethyl-5,6,7,8-tetrahydro-9,10-anthraquinone; H; 4; eAQH; 2; 2-ethyl-5,6,7,8-tetrahydro-9,10-anthrahydroquinone; Iso; -H; 4; eAQH; 2; 2-ethyl-1,2,3,4-tetrahydro-9,10-anthrahydroquinone; eAN; 2-ethylanthrone (2-ethyl-10-anthrone and 2-ethyl-9-anthrone); OXO; 2-ethyloxanthrone2-Ethyl-9,10-anthraquinone; Polyaniline; Palladium catalysts; Hydrogenation
Thermo catalytic decomposition of methane over Ni–Mg and Ni–Cu–Mg catalysts by Y. Echegoyen; I. Suelves; M.J. Lázaro; M.L. Sanjuán; R. Moliner (pp. 229-237).
In this paper we study the performance of Ni–Mg catalysts on hydrogen production by TCD of methane prepared by three different methods: co-precipitation, impregnation and fusion. The effect of Cu doping has also been analyzed. Catalysts and deposited carbon have been characterized by ICP-OES, XRD, SEM, TEM and Raman spectroscopy. Deposited carbon appears as fishbone type nanofibers. ▪Catalytic decomposition of methane is a potential alternative route for the production of hydrogen from natural gas. In the present paper we report the results of hydrogen production in the TCD of methane over Ni–Mg and Ni–Cu–Mg catalysts prepared by co-precipitation, impregnation and fusion methods. The characterization of the catalysts used and the carbon obtained is also presented. Whatever to be the preparation method, all the catalysts show a high and almost constant methane decomposition rate without deactivation after 8h on stream. The presence of copper enhances hydrogen production and the best results were obtained for Ni–Cu–Mg catalysts prepared by the fusion method, reaching a hydrogen production of 80vol.%. For the Ni–Mg catalysts, the nickel crystal size influences on the catalysts performance so that the highest the crystallite size the lowest the hydrogen yields. In contrast, for the Ni–Cu–Mg catalyst the Ni particle size has not a significant influence on the hydrogen yields. All catalysts tested promote formation of filamentous carbon some micrometers long and with a fiber diameter highly dependent on the presence of Cu: Ni–Mg catalysts promote the formation of fibers with homogeneous diameter around 30nm while Ni–Cu–Mg catalysts lead to the formation of fibers of inhomogeneous and bigger diameter.
Keywords: Hydrogen production; Methane; Ni–Mg catalysts
Solid acid catalysis of tandem isomerization-lactonization of olefinic acids by Yibo Zhou; L. Keith Woo; Robert J. Angelici (pp. 238-244).
The conversion of unsaturated acids to γ-lactones is catalyzed by the solid sulfonic acid catalysts Amberlyst-15 and Nafion SAC-13 in refluxing chlorobenzene. For 3- and 4-enoic acids, in which double bond migration is not required for γ-lactone formation, yields are 95–100%. For 5-, 6-, 9-, and 10-enoic acids, the lactone yield decreases from 95% to 25% as the distance between the olefin and carboxylic acid groups increases. Amberlyst-15 is the preferred catalyst in these reactions because of its lower cost and reusability.The 5-, 6-, 9-, and 10-enoic acids (a) undergo tandem olefin migration followed by cyclization to give γ-lactone (b) products in 25-95% yields in the presence of Amberlyst-15 in refluxing chlorobenzene. In all of these reactions, the δ-lactone (c) forms initially and then rearranges to the final γ-lactone (b) product.▪
Keywords: Lactonization; Tandem catalysis; Unsaturated carboxylic acids; Amberlyst-15; Nafion; ®
Effect of framework Si/Al ratio and extra-framework aluminum on the catalytic activity of Y zeolite by Bin Xu; Silvia Bordiga; Roel Prins; Jeroen A. van Bokhoven (pp. 245-253).
The effect of the Si/Al ratio of the framework on the intrinsic activity of Brønsted acid sites in Y zeolite was investigated by monomolecular cracking of propane and physicochemical characterization. Samples with different Si/Al ratios were obtained by synthesis and by post-synthesis treatments. Two samples with Si/Al ratios of 3.3 and 3.6 exhibited characteristic features similar to those of commercial Y zeolite with a Si/Al ratio of 2.6, but they were more stable. An ultrastable Y (HUSY) was treated with ammonia and ethylenediaminetetraacetic acid (EDTA) to remove extra-framework aluminum (EFAl). The rates per gram increased with Si/Al ratio, but the activation energies did not depend on the Si/Al ratio or on the presence of EFAl. This implies that the intrinsic activity of the Brønsted acid sites that participate in the reaction is identical in all the samples. The enhanced activity of the samples with Si/Al ratios up to 5.0 is attributed to the creation of more isolated Brønsted acid sites, which are active in this demanding reaction. The removal of EFAl did not affect the intrinsic catalytic activity but increased the number of catalytically active framework Brønsted acid sites.Not all tetrahedrally coordinated aluminum atoms contribute to active Brønsted acid sites in the monomolecular cracking of propane. Steaming and synthesis of high-silicon zeolite Y results in more isolated acid sites that contribute to activity. The intrinsic activity of the active sites is independent of synthesis and treatment procedures. ▪
Keywords: Y zeolite; High-silica Y; USY; Monomolecular cracking; Acidity; Steaming; Extra-framework aluminum
Selective hydrogenation of acetylene in the presence of ethylene on K+-β-zeolite supported Pd and PdAg catalysts by Wei Huang; William Pyrz; Raul F. Lobo; Jingguang G. Chen (pp. 254-263).
The K+-β-zeolite supported Pd and PdAg catalysts have been synthesized and evaluated using both FTIR batch reactor and flow reactor. The bimetallic PdAg catalyst shows much higher selectivity but lower activity for acetylene hydrogenation in presence of ethylene than the Pd monometallic catalyst. The novel K+-β-zeolite support led to an increase in selectivity due to the preferential adsorption of acetylene over ethylene. This support is superior to the γ-Al2O3 and Na+-β-zeolite used in our previous studies. ▪The selective hydrogenation of acetylene in the presence of ethylene has been studied on K+ exchanged β-zeolite supported Pd and PdAg catalysts. Results from batch reactor studies with Fourier transform infrared spectroscopy (FTIR) have shown that the K+-β-zeolite support is more selective than the Al2O3 or Na+-β-zeolite supports toward the hydrogenation of acetylene. The rate and equilibrium constants for Pd/K+-β-zeolite and PdAg/K+-β-zeolite were determined using a Langmuir–Hinshelwood model. The selectivity of the PdAg bimetallic catalyst is twice of that of the Pd catalyst. Results from flow reactor studies show that the PdAg/K+-β-zeolite catalyst has higher selectivity but lower activity toward acetylene hydrogenation than the Pd/K+-β-zeolite catalyst. The selectivity to the undesirable ethane by-product is inhibited on the bimetallic catalyst. Extended X-ray absorption fine structure (EXAFS) studies and transmission electron microscope (TEM) analysis confirm the formation of Pd–Ag bimetallic bonds in the PdAg/K+-β-zeolite catalyst.
Keywords: Selective hydrogenation; Acetylene; Ethylene; Pd; Pd–Ag; Bimetallic catalysts; K; +; -β-zeolite; EXAFS; TEM; FTIR
Synthesis and characterization of ZrO2–TiO2 binary oxide semiconductor nanoparticles: Application and interparticle electron transfer process by Bernaurdshaw Neppolian; Qiliang Wang; Hiromi Yamashita; Heechul Choi (pp. 264-271).
The chemical interaction of Zr–O–Ti in the binary oxide catalysts is found to be a major factor in high performance for the degradation of 4-CP. Photoluminescence provides strong evidence for the existence of the ZrO2 CB surface trap states which lie below the CB of TiO2 and facilitate fast electrons injection to the CB of TiO2 and which prevent the recombination of electrons and holes.▪A series of nanocrystalline mesoporous ZrO2–TiO2 binary oxide photocatalysts with different wt% of ZrO2 and TiO2 were prepared by a sol–gel method. These binary oxide photocatalysts were characterized by XRD, N2 adsorption–desorption, DRS, FTIR, Raman spectroscopy, photoluminescence and TEM analyses. Detailed investigations revealed that the ZrO2–TiO2 catalysts are highly micro-crystalline in nature with a larger surface area than that of the pure TiO2 or ZrO2 catalysts since the added ZrO2 plays an important role in promoting the formation of nanoparticles with an anatase structure, high surface area and acidity. The photocatalytic reactivity of the catalysts was investigated for the degradation of 4-chlorophenol in an aqueous phase in which the ZrO2–TiO2 photocatalysts were found to exhibit remarkably higher photocatalytic reactivity than that of pure TiO2 and ZrO2. The catalytic activity of the binary oxide photocatalysts for the degradation of 4-chlorophenol was observed to be gradually enhanced with an increase in the ZrO2 content and reached an optimum at 12wt% of ZrO2 while maintaining the same percentage degradation with further loading of ZrO2 until 50wt%. Such high reactivity is due to the easy transfer of the photo-formed electrons from the conduction band surface trap states of ZrO2 to the conduction band of TiO2 through strong chemical interactions, thereby, preventing the radiative recombination of the photo-formed electrons and holes. The ZrO2–TiO2 catalysts were, thus, found to be highly active for the efficient degradation of 4-chlorophenol and, in fact, exhibited just as efficient activity as the commercial P-25, Degussa TiO2 catalysts, and a new reaction mechanism has, hereby, been proposed.
Keywords: TiO; 2; ZrO; 2; ZrO; 2; –TiO; 2; binary oxide photocatalysts; 4-Chlorophenol
Nanosized sulfated SnO2 dispersed in the micropores of Al-pillared clay as an efficient catalyst for the synthesis of some biologically important molecules by M. Sowmiya; Aditya Sharma; Sarang Parsodkar; B.G. Mishra; Amit Dubey (pp. 272-280).
Nanosize sulfated tin oxide dispersed in the micropores of Al-pillared clay has been demonstrated as an efficient catalyst for the benign solvent-free synthesis of 3,4-dihydropyrimidin-2(1 H)-ones, thiochromans, selective protection of aldehyde groups as 1,1-diacetates and coumarins. The protocol developed using the nanosize catalyst offer many advantages in terms of simple experimentation, short reaction time, solvent-free conditions, catalyst reusability, high yield and purity of the products. ▪Nanosized sulfated tin oxide (STO) particles dispersed in the micropores of Al-pillared clay were prepared by a precipitation–deposition method followed by heat treatment and sulfation. The Al-pillared clays (Al-P) was prepared by the intercalation of [Al13O4(OH)24(H2O)12]7+ clusters into the clay interlayers. The physicochemical characteristics of the STO/Al-P material were evaluated by using X-ray diffraction (XRD), infrared (IR), transmission electron microscopy (TEM) and sorptometric studies. XRD results indicate an expansion in the interlayer spacing upon pillaring. The layer structure is found to be retained after the dispersion of the STO particles. The TEM images indicate the presence of uniform STO particles with sizes in the 5–15nm range. The sorptometric study show a type I isotherm for both the Al-P and STO/Al-P material, indicating the presence of micropores. The pore volume of the parent-pillared clay was found to decrease upon supporting the STO particles. The STO/Al-P material was used as an environmentally benign, recyclable and efficient catalyst for the solvent-free synthesis of 3,4-dihydropyrimidin-2(1 H)-ones, thiochromans, with selective protection of aldehyde groups such as 1,1-diacetates and coumarins. The STO/Al-P catalyst was highly active for the synthesis of the above-mentioned molecules. The protocol developed using this catalyst has many advantages over those of the conventional mineral acids used as catalysts.
Keywords: Pillared clay; Sulfated tin oxide; 3,4-Dihydropyrimidin-2(1; H; )-ones; Coumarins; Thiochromans; 1,1-Diacetates
Support effects on Ru–HPA bifunctional catalysts: Surface characterization and catalytic performance by B. Bachiller-Baeza; J. Alvarez-Rodríguez; A. Guerrero-Ruiz; I. Rodríguez-Ramos (pp. 281-289).
The behaviour of three metal–acid bifunctional catalysts, where the metal was Ru and the acid function was a heteropolyacid (HPA), was compared in the hydroconversion of n-hexane. Both the activity and the selectivity pattern depended on the used support: silica, high surface area graphite (HSAG) or zeolite KL. The series of techniques applied to characterize the catalysts have shown that the selection of the support affects the acid sites strength distributions as well as the interaction between the Ru precursor and the HPA support. ▪The behaviour of three metal–acid bifunctional catalysts, where the metal was Ru and the acid function was a heteropolyacid (HPA), was compared in the hydroconversion of n-hexane. Both the activity and the selectivity pattern depended on the used support: silica, high surface area graphite (HSAG) or zeolite KL. While Ru–HPA–SiO2 gave selectivity to isomerization products of 97%, the Ru–HPA–KL sample gave a selectivity of 96% to hydrogenolysis products. And, the performance of Ru–HPA–HSAG lied between that for Ru–HPA–SiO2 and Ru–HPA–KL, giving both isomerization and hydrogenolysis products, with selectivities of 45 and 54%, respectively. The series of techniques applied to characterize the catalysts have assisted in understanding the catalytic performance. The HPA phase has been detected over all the HPA-modified supports, but different acid sites strength distributions have been determined by calorimetry of NH3 adsorption, following the order HPA–SiO2>HPA–HSAG>HPA–KL. Also, different Ru species have been observed on the catalysts surface due to the interaction between the Ru precursor and the HPA support. Finally, the analysis of the results has suggested that the support determines the role played by both metal and acid functions, which separately would lead to hydrogenolysis and isomerization reactions, respectively.
Keywords: Heteropolyacid; Bifunctional catalysts; n; -Hexane hydroconversion