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Applied Catalysis A, General (v.320, #)
Vanadyl phosphate catalysts in biodiesel production by M. Di Serio; M. Cozzolino; R. Tesser; P. Patrono; F. Pinzari; B. Bonelli; E. Santacesaria (pp. 1-7).
Vanadium phosphate (VOP) catalysts resulted very active in the transesterification reaction of triglycerides with methanol. A slow deactivation of the catalysts has been observed but the catalyst can easily be regenerated by calcination in air. The characterization results showed that the deactivation is due to a progressive reduction of vanadium species from V5+ to V4+ and V3+ by methanol. VOP catalysts could already be used industrially for biodiesel production but their performances can probably be greatly improved in perspective. ▪The possibility of using vanadyl phosphate (VOP)-based catalysts in biodiesel production has been investigated. Vanadium phosphate catalysts resulted very active in the transesterification reaction of triglycerides with methanol, despite their low specific surface area. A slow deactivation of the catalysts has been experimentally detected under the reaction conditions, but the catalyst can easily be regenerated by calcinations in air. The influence of the calcination treatment on the surface structure and, consequently, on its catalytic performances was deeply investigated. Both fresh and used catalysts were characterized by using several techniques, such as BET, X-ray diffraction (XRD), UV–vis diffuse reflectance (DRUV) and laser-Raman (LRS). The characterization results showed that the deactivation is due to a progressive reduction of vanadium (V) species from V5+ to V4+ and V3+ by methanol. By comparing the obtained performances of VOP catalysts with the ones of other heterogeneous catalysts reported by the literature, it is possible to conclude that VOP catalysts can already be used industrially for biodiesel production but their performances can probably be greatly improved in perspective.
Keywords: Transesterification; Biodiesel; Vanadyl phosphate; Heterogeneous catalysis
Nitrogen poisoning effect on the catalytic cracking of gasoil by G. Caeiro; A.F. Costa; H.S. Cerqueira; P. Magnoux; J.M. Lopes; P. Matias; F. Ramôa Ribeiro (pp. 8-15).
This work consisted in the assessment of the effect of basic nitrogen in catalytic cracking. Laboratory evaluation was done with four feedstocks with distinct nitrogen contents, some of them prepared by quinoline addition. Basic nitrogen reduces the conversion in 5–10wt% points. Nitrogen contained in quinoline molecules had similar effects to the one present in the original gasoil. ▪This research work consisted in the assessment of the damaging effect of basic nitrogen in the performance of industrial catalytic cracking catalysts. Laboratory evaluation of an industrial equilibrium catalyst was done with four feedstocks with very distinct nitrogen contents: a gasoil with 1307ppm of basic N (feedstock A); feedstock A after an acid treatment with the objective of partially removing the basic nitrogen (feedstock B: 135ppm of basic N); feedstock B after adding 1172ppm of quinoline (feedstock C: 1307ppm of basic N); and feedstock A after adding 1172ppm of quinoline (feedstock D: 2479ppm of basic N). Characterization of the gasoils showed that only the basic nitrogen content was affected by the acid treatment. The evaluation results showed that basic nitrogen reduces the gasoil cracking conversion in 5–10wt% points, depending on the catalyst to oil ratio. In addition, at constant conversion, the increase in basic nitrogen content also resulted both in a decrease in gasoline yield and an increase in coke and hydrogen yields. Nitrogen contained in the quinoline molecule had similar effects to that present in the original gasoil.
Keywords: Catalytic cracking; Vacuum gasoil; Nitrogen poisoning; Acid treatment; Equilibrium catalyst
Real-time principal component analysis of in-line NIR spectroscopic data as applied to heterogeneous catalysis research by Margaret J. Strauss; Nicolaas M. Prinsloo (pp. 16-23).
A new methodology for monitoring a catalytic reaction in a continuous bench scale reactor is presented. It uses an in-line near infrared spectrometer to analyse the product. This is followed by principal component analysis which converts a spectrum to a point on a three-dimensional score plot. With a new spectrum being processed every few minutes, a picture of what is happening to the product in real-time evolves. This is a qualitative assessment of the reaction and enables the identification of periods of stability and process disturbances. No time-consuming calibrations or prior knowledge of the ideal near infrared product spectrum is required.The paper discusses this new methodology and illustrates its success with three case studies. It is shown how the method can be used to identify process changes or disturbances quickly, to recognise periods of stability and to detect problems such as rapid catalyst deactivation. Catalyst test runs can now be conducted much faster and more efficiently.A new methodology for monitoring a catalytic reaction in a continuous bench scale reactor is presented. It uses an in-line near infrared spectrometer to analyse the product. This is followed by principal component analysis which converts a spectrum to a point on a three-dimensional score plot. This allows a qualitative assessment of the reaction and enables the identification of periods of stability and process disturbances. ▪
Keywords: Catalysis; Near infrared spectroscopy; Principal component analysis
Production of hydrogen from catalytic steam reforming of bio-oil using C12A7-O−-based catalysts by Zhaoxiang Wang; Yue Pan; Ting Dong; Xifeng Zhu; Tao Kan; Lixia Yuan; Youshifumi Torimoto; Masayoshi Sadakata; Quanxin Li (pp. 24-34).
The production of hydrogen from the catalytic steam reforming of the bio-oil was investigated by using novel metal-doped catalysts of [Ca24Al28O64]4+·4O−/M (C12A7-O−/M, M=Mg, K, Ce). The catalyst characteristics and the intermediate species formed in the steam reforming processes were investigated by XRD, XPS, ICP-AES and FT-IR measurements. The mechanism of the bio-oil steam reforming was also addressed. ▪The production of hydrogen from the catalytic steam reforming of bio-oil, generated from fast pyrolysis of biomass, was investigated by using novel metal-doped catalysts of [Ca24Al28O64]4+·4O−/M (C12A7-O−/M, M=Mg, K, Ce). The features of the steam reforming of the bio-oil, including the effects of temperature, the metal-doped content and the S/C ratio (the ratio of mol steam to mol carbon fed) on the hydrogen yield, carbon conversion (mol carbon in production gases to mol carbon fed) and the distributions of the products were measured in the fixed-bed continuous flow reactor. It was found that the C12A7-O−/18% Mg catalyst gave the highest yield of hydrogen and the best carbon conversion among our tested catalysts. For the C12A7-O−/18% Mg catalyst, a hydrogen yield as high as 80% was obtained, and the maximum carbon conversion is up to 96% under the steam reforming condition (S/C>4.0, GHSV=10,000h−1, T=750°C). The catalyst deactivation was mainly caused by the deposition of carbon (coke-formation). Initial catalyst activity can be partly maintained through periodic regeneration via the cleaning of the catalyst and the gasification of the carbon deposits. The catalyst characteristics and the intermediate species formed in the steam reforming processes were investigated by the XRD, XPS, ICP-AES and FT-IR measurements. The mechanism of the bio-oil steam reforming was addressed according to the above investigations.
Keywords: C12A7-O; −; /M; Bio-oil; Steam reforming; Hydrogen
Vapor phase acylation of phenol with ethyl acetate over H3PO4/TiO2-ZrO2 by M. Ghiaci; R.J. Kalbasi; M. Mollahasani; H. Aghaei (pp. 35-42).
Vapor phase acylation of phenol with ethyl acetate over 15wt.% H3PO4/TiO2-ZrO2-surf has been investigated. In this reaction, 2-hydroxy acetophenone was found to be the major product when 4-hydroxy acetophenone was not detected in the product stream; phenyl acetate and alkylated products were the minor products. ▪ZrO2-TiO2 mixed oxides with a Ti and Zr molar ratio of 1/1 were prepared with and without surfactant by the sol–gel method. Catalysts containing 5–35% H3PO4 were prepared using these mixed oxides and the catalytic performance of each material for vapor phase acylation of phenol to 2-hydroxy acetophenone (2-HAP) was determined. During the reaction of phenol with ethyl acetate, 2-HAP was found to be the major product, when 4-hydroxy acetophenone was not detected in the product stream; phenylacetate (PA) and alkylated products were the minor products. In the best experimental conditions, the alkylated products were less than 0.5%. This reaction may represent an environmentally friendly alternative to use the ethyl acetate as the acylating reagent. The feed molar ratios of phenol/ethyl acetate were varied over a wide range (1–0.1), and the optimum feed ratio of phenol/ethyl acetate was 1:3. Space velocity employed in phenol acylation reported as WHSV (phenol)=1.35h−1. The acylation reactions were carried out in the temperature range of 473–673K and the optimum H3PO4 content for acylation was 15wt.% H3PO4.
Keywords: Vapor phase; Acylation; Phenol; Ethyl acetate; Hydroxy acetophenone; Environmentally friendly
Wet impregnation of alumina-washcoated monoliths: Effect of the drying procedure on Ni distribution and on autothermal reforming activity by L. Villegas; F. Masset; N. Guilhaume (pp. 43-55).
The preparation procedure of catalytic cordierite monoliths was studied, from the washcoating with alumina to the deposition of Ni by wet impregnation. The effect of drying (oven, room temperature or microwaves drying) on Ni distribution was investigated, and the monoliths were characterised by various techniques. The monolithic catalysts were tested in autothermal reforming of isooctane and the coke deposits characterised.▪The complete preparation procedure of catalytic cordierite monoliths has been studied, from the washcoating with alumina to the deposition of Ni by wet impregnation. The effect of drying (oven, room temperature or microwaves drying) on Ni distribution was investigated by SEM, TEM, XPS and surface area measurements.The use of γ-Al2O3 suspensions of suitable particles size allows a faster alumina loading and the deposition of a washcoat layer with better adhesion properties than those obtained with boehmite precursors.The Ni distribution is strongly influenced by drying method applied to wet-impregnated monoliths. At a macroscopic scale, the Ni distribution is more homogeneous after microwaves or room temperature drying. At a microscopic scale, there is a surface enrichment of the washcoat in Ni, whatever the drying method applied. In all catalysts, the Ni is present in two forms: it is predominantly incorporated in a Ni-alumina spinel phase, but some large metal particles (10–20nm) are also present, in a larger extent in the monoliths dried by microwaves and oven procedures.All monoliths deactivate slowly with time on stream during ATR of isooctane, but the oven-dried monoliths deactivate more markedly. Amorphous carbon film and whiskers were identified on all catalysts. The deactivation is not directly related to the total amount of deposited coke, but rather to the type of carbon and to Ni dispersion at both microscopic (large/small Ni particles) and macroscopic (axial Ni distribution in the channels) scales.
Keywords: Monolith; Alumina washcoat; Ni catalyst; Hydrogen production; Autothermal reforming
Re(VII) oxide on mesoporous alumina of different types—Activity in the metathesis of olefins and their oxygen-containing derivatives by Hynek Balcar; Roman Hamtil; Naděžda Žilková; Zhaorong Zhang; Thomas J. Pinnavaia; Jiří Čejka (pp. 56-63).
Heterogeneous catalysts for metathesis of olefins and their oxygen-containing derivatives were prepared by supporting Re(VII) oxide on (i) mesostructured γ-aluminas with lath-like and scaffold-like morphologies and (ii) organized mesoporous alumina with wormhole-like pore structure.▪Advanced heterogeneous catalysts for olefin metathesis were prepared by supporting Re(VII) oxide on (i) mesostructured γ-aluminas with lath-like and scaffold-like morphologies and (ii) organized mesoporous alumina with wormhole-like pore structure. The thermal spreading method was found to be very suitable technique for preparation of a highly active catalyst. In the case of dec-1-ene metathesis, Re(VII) oxide catalysts supported on mesoporous aluminas exhibited a high activity and selectivity independently of the type of catalyst support. For metathesis of olefin functional derivatives, namely p-allylanisole and diethyl diallylmalonate, the activity of Re(VII) catalysts with optimum amount of Re(VII) being 9.0wt% (with Me4Sn as co-catalyst) was found to depend on the catalyst pore size. Catalyst prepared from mesoporous aluminas with pore sizes at least 4.0nm exhibited much higher conversions of substrates compared with catalysts of 3.5nm pores.
Keywords: Organized mesoporous alumina; Metathesis; Olefin functional derivatives; Rhenium oxide
Selective mono- N-methylation of aniline substrates on Cu1− xZn xFe2O4 by Munusamy Vijayaraj; Chinnakonda S. Gopinath (pp. 64-68).
Selective mono- N-methylation of substituted anilines ( o-, m- and p-toluidines, 2,6-xylidine, p-anisidine and p-aminoacetophenone) was carried out with methanol as methylating agent under vapor phase reaction conditions on Cu1− xZn xFe2O4 systems. The catalytic reactions with each aniline substrate were carried out at optimum reaction conditions (MeOH:anilines:water=3:1:1, space velocity=3.58h−1) between 543 and 603K. The presence of a ring-directing group did not have any significant influence on the N-methylaniline(s) selectivity, which remains very high; the same initial conversion/yield was observed for at least 11h. Electronic effects due to different groups in the above aniline substrates influence the reactivity of the substrates in terms of conversion and yield. Toluidine reactivity varies with respect to the position ( ortho, meta and para) of the methyl group on the phenyl ring. Para-substituted anilines ( p-toluidine and p-anisidine) exhibit comparable catalytic activity, while p-aminoacetophenone shows higher conversion. The perpendicular orientation of toluidine substrates on catalyst surfaces influences the conversion and N-methyltoluidine yield. Increased crowding at ortho-position and hence steric hindrance (aniline> o-toluidine>2,6-xylidine) restrict the substrates interaction with the catalyst surface, and 2,6-xylidine shows no reactivity. The best catalytic activity observed with Cu0.5Zn0.5Fe2O4 was due to a heterogeneous distribution of metal ions on the surface with Zn serving as active spacer group as well as methyl species source.The influence of various substituted anilines towards mono- N-methylated products were examined on Cu0.5Zn0.5Fe2O4 catalyst under optimum reaction conditions. Although no significant influence on high selectivity was observed, there is a change in conversion and yield observed depending on the substituent and its position on the aromatic ring. Meta-toluidine and aniline shows a comparable activity. ▪
Keywords: N; -methylation; Spinel; Selective; N; -methylation; N; -methylaniline; Mono-; N; -methylation
Reaction mechanism of 4,6-dimethyldibenzothiophene desulfurization over sulfided NiMoP/Al2O3-zeolite catalysts by F. Richard; T. Boita; G. Pérot (pp. 69-79).
The desulfurization of 4,6-dimethyldibenzothiophene (4,6-DMDBT) was carried out over a pure sulfided NiMoP/Al2O3 catalyst and over mechanical mixtures containing sulfided NiMoP/Al2O3 and an acidic component such as HY and Hβ zeolites at 340°C under 4MPa of total pressure in a fixed bed reactor. The transformation of 4,6-DMDBT was also carried out over HY and Hβ zeolites at 350°C under atmospheric pressure.Over the pure sulfided NiMoP/Al2O3 catalyst, 4,6-DMDBT transformed mainly through two pathways: direct desulfurization leading to 3,3′-dimethylbiphenyl (3,3′-DMBPh) and desulfurization after hydrogenation (HYD) leading to 3-(3′-methylcyclohexyl)toluene (3,3′-MCHT).Over pure zeolites, 4,6-DMDBT underwent both isomerization and disproportionation reactions. Hβ was more selective in isomerization than HY.The use of mechanical mixtures (sulfided NiMoP/Al2O3-zeolite) as bifunctional catalysts allowed an increase of the 4,6-DMDBT reactivity which depended on the acidity and the porosity of the zeolite. Over these bifunctional catalysts, two new categories of products were observed: isomerization and disproportionation products resulting from acidic catalysis and products resulting from their desulfurization. The products obtained by isomerization and disproportionation reactions, which presented approximately the same reactivity in hydrodesulfurization, were more reactive than 4,6-DMDBT. The NiMoP/Al2O3 sulfided catalyst associated with HY-16 zeolite (Si/Al ratio=16) was the most active of all the mechanical mixtures used for the desulfurization of 4,6-DMDBT. Indeed, HY-16 was the most active zeolite both in isomerization and disproportionation reactions.The desulfurization of 4,6-dimethyldibenzothiophene (4,6-DMDBT) was carried out over a sulfided NiMoP/Al2O3 catalyst and over mechanical mixtures containing NiMoP/Al2O3 and an acidic component such as HY and Hβ zeolites at 340°C under 4MPa of total pressure. The use of mechanical mixtures (NiMoP/Al2O3-zeolite) as bifunctional catalysts allowed an increase of the 4,6-DMDBT reactivity which depended on the acidity and the porosity of the zeolite.▪
Keywords: Zeolites; NiMoP/Al; 2; O; 3; 4,6-Dimethyldibenzothiophene; Hydrodesulfurization; Isomerization; Disproportionation
Pt/ZrO2/TiO2 catalysts for selective hydrogenation of crotonaldehyde: Tuning the SMSI effect for optimum performance by A.M. Ruppert; T. Paryjczak (pp. 80-90).
Gas phase hydrogenation of crotonaldehyde was performed over Pt/ZrO2/TiO2 catalysts calcined at 200 or 400°C and reduced at 200–600°C. The catalysts were thoroughly characterised after different stages of pretreatment. Pt/30% ZrO2/TiO2 calcined at 200°C and reduced at 500°C showed the highest crotyl alcohol selectivity (50%) while retaining good activity. We explain it by the mutually opposing action of two factors – presence of ZrO2 and ‘permeability’ of Pt phase for TiO x migration – in controlling the SMSI effect. ▪Gas phase hydrogenation of crotonaldehyde was performed over Pt/ZrO2/TiO2 catalysts with different zirconia loadings, subjected to low- and high-temperature calcination (200 and 400°C) and a range of reduction temperatures (200–600°C). Pt/TiO2 was used as reference system. The catalysts were characterised by TPR, XPS, SEM, HR TEM, TOF-SIMS and H2, O2 and CO chemisorption after different stages of thermal pretreatments. The relationship between catalytic activity, selectivity towards crotyl alcohol and physicochemical properties of the catalysts was examined. The catalyst containing 30% ZrO2 in the support, calcined at 200°C and reduced at 500°C showed the highest selectivity (50%) while retaining good activity. The explanation of those properties was proposed, involving the mutually opposing action of two factors – presence of ZrO2 and ‘permeability’ of Pt phase for TiO x migration – in controlling of the SMSI effect.
Keywords: Crotonaldehyde; Hydrogenation; Platinum; Zirconia; Titania; Pt/ZrO; 2; /TiO; 2; SMSI
The role of additives in the catalytic reduction of NO by CO over Pd-In/SiO2 and Pd-Pb/SiO2 catalysts by Takashi Hirano; Yoshiyuki Ozawa; Takayuki Sekido; Takashi Ogino; Toshihiro Miyao; Shuichi Naito (pp. 91-97).
Formation of intermetallic compounds was observed in the cases of both Pd-In/SiO2 and Pd-Pb/SiO2 catalysts, which caused a drastic enhancement of the reaction rate of N2O formation. By adding In or Pb, a new reaction pathway is opened via NO dimer-like intermediates, and the role of additives is the stabilization of these unique intermediates on the slightly oxidized intermetallic compound.▪Addition effect of In and Pb on the NO-CO reaction over SiO2 supported Pd catalysts was studied, using a closed gas circulation system as well as in situ infrared, XRD and XPS spectroscopies. Formation of intermetallic compounds was observed in the cases of both Pd-In/SiO2 and Pd-Pb/SiO2 catalysts. These compounds caused a drastic enhancement of the reaction rate of N2O formation. Infrared analyses revealed the weakening of CO adsorption on Pd metal by the formation of intermetallic compounds, which is the main reason of the enhancement of reaction rate. Over Pd/SiO2, the reaction may proceed via redox mechanism through NO dissociation to form the oxidized surface, followed by its reduction with CO. By adding In or Pb, a new reaction pathway is opened at the lower temperature region via NO dimer-like intermediates. The role of additives is the stabilization of these unique intermediates on the slightly oxidized intermetallic compound surfaces.
Keywords: NO-CO reaction; Pd/SiO; 2; catalyst; Addition effect; Pd-In; Pd-Pb
CO methanation over supported bimetallic Ni–Fe catalysts: From computational studies towards catalyst optimization by A.L. Kustov; A.M. Frey; K.E. Larsen; T. Johannessen; J.K. Nørskov; C.H. Christensen (pp. 98-104).
DFT calculations combined with a computational screening method have previously shown that bimetallic Ni–Fe alloys should be more active than the traditional Ni-based catalyst for CO methanation. That was confirmed experimentally for a number of bimetallic Ni–Fe catalysts supported on MgAl2O4. Here, we report a more detailed catalytic study aimed at optimizing the catalyst performance. For this purpose, two series of mono and bimetallic Ni–Fe catalysts supported on MgAl2O4 and Al2O3, respectively, were prepared. All catalysts were tested in the CO methanation reaction in the temperature interval 200–300°C, and characterized using elemental analysis, N2 physisorption measurements, XRD and TEM. Optimization of the catalyst performance was made by varying the Ni:Fe ratio, the total metal loading and the support material. For both support materials, the bimetallic catalysts with compositions 25Fe75Ni and 50Fe50Ni showed significantly better activity and in some cases also a higher selectivity to methane compared with the traditional monometallic Ni and Fe catalysts. A catalyst with composition 25Fe75Ni was found to be the most active in CO hydrogenation for the MgAl2O4 support at low metal loadings. At high metal concentrations, the maximum for the methanation activity was found for catalysts with composition 50Ni50Fe both on the MgAl2O4 and Al2O3 supports. This difference can be attributed to a higher reducibility of the constituting metals with increasing metal concentration. The maximum of the catalytic activity and the highest selectivity to methane were observed for the sample with 20wt% total metal loading. It appears that it is possible to increase substantially the efficiency of Ni-based methanation catalyst by alloying with Fe.In accordance with predictions from computation screening studies, it is shown that alloyed Fe–Ni catalysts are superior to the pure Fe and Ni catalysts in the methanation reaction. The influence of the support material, the alloy composition and the total metal content is investigated to identify the best catalyst for industrial applications.▪
Keywords: Methanation; Nickel; Iron; Bimetallic catalyst; Interpolation concept
Catalytic steam reforming of dimethyl ether (DME) over high surface area Ce–ZrO2 at SOFC temperature: The possible use of DME in indirect internal reforming operation (IIR-SOFC) by N. Laosiripojana; S. Assabumrungrat (pp. 105-113).
High surface area Ce–ZrO2 reform DME efficiently producing H2, CO, and CH4 without CH3OH presented in the product gas. The combination use of Ce–ZrO2 along with Ni/Al2O3 was proven to improve the reforming performance. IIR-SOFC model was then studied by initially feed DME to Ce–ZrO2–Ni/Al2O3 before reaching Ni/YSZ. The yield of hydrogen from this configuration was high, and the degree of carbon formation on the surface of Ni/YSZ was significantly low. Steam reforming of DME over IIR configuration at 900oC (non-catalyst/Ni/YSZ (▴), Ce–ZrO2/Ni/YSZ (●), Ni/Al2O3/Ni/YSZ (×), Ce–ZrO2+Ni/Al2O3/Ni/YSZ (▵), and Ce–ZrO2–Ni/Al2O3/Ni/YSZ (○)) (4kPa DME, and 12kPa H2O).▪This study was aimed at developing a suitable reforming catalyst for later application in an indirect internal reforming solid oxide fuel cell (IIR-SOFC) fuelled by dimethyl ether (DME). It was found that, at temperature higher than 800°C, DME decomposed homogeneously, producing CH4 and CH3OH with small amount of CO, CO2, and H2. High surface area Ce–ZrO2 can reform DME with steam efficiently at 900°C, producing high contents of H2, CO, and CH4 without the presence of CH3OH in the product gas. The combination use of Ce–ZrO2 (as a pre-reforming catalyst) and Ni/Al2O3 in the single unit was proven to significantly improve the reforming performance. According to this combination, the role of Ce–ZrO2 is to first decompose CH3OH and some CH4 generated from the homogeneous decomposition of DME, while the role of Ni/Al2O3 is to reform CH4 left from the pre-reforming section and to maximize the yield of H2 production.As another approach, IIR-SOFC model was studied using an annular ceramic reactor, in which DME initially reacted with steam on Ce–ZrO2+Ni/Al2O3 at the inner side of the reactor and then Ni/YSZ at the outer side. The stability and the yield of hydrogen production over this configuration were considerably higher than those of systems packed with single Ce–ZrO2, single Ni/Al2O3, and without the filling of catalyst. In addition, the degree of carbon formation on the surface of Ni/YSZ was significantly low. The successful development of this reforming pattern improves the efficiency of IIR-SOFC fueled by DME by eliminating the requirement of an external reforming unit installation.
Keywords: Indirect internal reforming; Dimethyl ether; Ce–ZrO; 2; Solid oxide fuel cell
The influence of cooling atmosphere after reduction on the catalytic properties of Au/Al2O3 and Au/MgO catalysts in CO oxidation by Ervin Gy. Szabó; András Tompos; Mihály Hegedűs; Ágnes Szegedi; József L. Margitfalvi (pp. 114-121).
Unexpected activity alterations were observed in CO oxidation upon changing the atmosphere of cooling from an inert gas to hydrogen after reduction in hydrogen at 350°C. Different supports resulted in different trends, e.g. over Au/MgO higher activities were obtained after cooling in helium, while Au/Al2O3 showed the opposite effect, i.e., higher activities were measured after cooling in hydrogen. The higher the Au content of the catalyst the more pronounced the “cooling effect”. Contrary to pure Au/Al2O3 catalysts the addition of redox-type modifiers, such as iron, manganese and cobalt to the support, the cooling in hydrogen decreased the activity. In situ FTIR results indicated that cooling in hydrogen increases the negative charge on the supported gold nanoparticles on both supports.Unexpected activity alterations were observed in CO oxidation upon changing the atmosphere of cooling from an inert gas to hydrogen after reduction in hydrogen at 350°C. Different supports resulted in different trends, e.g. over Au/MgO higher activities were obtained after cooling in helium, while Au/Al2O3 showed the opposite effect, i.e., higher activities were measured after cooling in hydrogen. ▪
Keywords: Au/MgO; Au/Al; 2; O; 3; Modified supported gold catalysts; CO oxidation; FTIR; Cooling effect
Ketones from acid condensation using supported CeO2 catalysts: Effect of additives by Kerry M. Dooley; Arvind K. Bhat; Craig P. Plaisance; Amitava D. Roy (pp. 122-133).
Metal-doped, supported CeO2/Al2O3 catalysts are effective for the high temperature decarboxylative condensation of carboxylic acids to produce ketones. Catalysts were characterized by H2 chemisorption, thermogravimetric reduction and coke analysis, and X-ray absorption spectroscopies. Product distributions in the reaction to MNK for such catalysts are shown (Y=molar yield to MNK). ▪Metal-doped, supported CeO2/Al2O3 catalysts are effective for the high temperature decarboxylative condensation of carboxylic acids to produce ketones. Representative catalysts were characterized based on H2 chemisorption, thermogravimetric reduction and coke analysis, and X-ray absorption spectroscopies at the Ce LIII-, K and Co K-, and Pd LIII-edges.Supported (on Al2O3) CeO2 (∼15–20wt.%) catalysts selectively catalyze the condensation of isobutyric acid to diisopropyl ketone and that of acetic acid and decanoic acid to methylnonylketone. Catalysts are stable in long-term operation, with periodic regeneration. The optimal temperature range is 470–480°C for the former reaction and 400–420°C for the latter. For the former reaction, doping supported CeO2 catalysts with most transition metals, or with strongly basic or acidic additives, catalyzed a variety of side reactions, but the addition of small amounts of Co that dissolved in CeO x could increase the yield to desired ketone. For the latter reaction, certain group VIII metals added to CeO2 catalysts in higher concentrations proved beneficial, particularly Co or Pd.
Keywords: Acid condensation; Non-symmetric ketone; Cerium oxide catalyst
Influence of silica calcination temperature on the performance of supported catalyst SiO2– nBuSnCl3/MAO/( nBuCp)2ZrCl2 polymerizing ethylene without separately feeding the MAO cocatalyst by M. Atiqullah; M.N. Akhtar; A.A. Moman; A.H. Abu-Raqabah; S.J. Palackal; H.A. Al-Muallem; O.M. Hamed (pp. 134-143).
The effects of silica calcination temperature on the performance of the supported catalyst [silica ES70– nBuSnCl3/MAO/( nBuCp)2ZrCl2] were studied by polymerizing ethylene without separately feeding the MAO cocatalyst. The catalyst activity, as a function of the calcination temperature, varied as follows: 250°C>600°C>800°C>450°C. ▪The effects of support calcination temperature, an important catalyst synthesis parameter, on the overall performance of the supported catalyst [silica ES70– nBuSnCl3/MAO/( nBuCp)2ZrCl2], polymerizing ethylene without separately feeding the MAO cocatalyst, were studied. The silica was calcined at 250, 450, 600, and 800°C for 4h. nBuSnCl3 was used to functionalize the silica.Ethylene was polymerized using the synthesized catalysts at 8.5bar(g) in hexane for 1h. No reactor fouling was observed. Free-flowing polymer particles with bulk density (0.23–0.27g/ml) and a fairly spherical morphology similar to that of the catalyst particles were obtained. Also, the particle size distribution of the polymer resembled that of the catalyst. Therefore, the replication phenomenon from catalyst to polymer took place. The narrow PSD span (1.41) indicates that the resulting polyethylenes are suitable for various mixing-intensive polymer applications. The MAO cocatalyst-free ethylene polymerization instantaneously formed a polymer film around the catalyst particle, which coated/immobilized the catalyst constituents; this is how leaching was in situ prevented which favored heterogeneous catalysis to occur. The catalysts showed fairly stable polymerization kinetics. The catalyst activity, as a function of the silica calcination temperature, varied as follows: 250°C>600°C>800°C>450°C. This finding has been explained considering the relevant surface chemistry phenomena. The calcination temperature did not significantly affect the bulk density and the PDI (3.4≤PDI≤3.8) of the resulting polyethylenes. The low PDI substantiates the retention of single-site catalytic behavior of the experimental supported catalysts.
Keywords: Supported zirconocene catalysts; Silica functionalization; Calcination temperature; Particle size distribution; Bulk density
The effects of iron addition to Pd/C and Pd+Pt/C catalysts on the selective hydrogenation of nitric acid in the presence of GeO2 by Takuma Hara; Yosuke Nakamura; Jun Nishimura (pp. 144-151).
Upon the selective catalytic hydrogenation of nitric acid to hydroxylamine, among various metal elements examine, iron was found to be particularly effective for improving the catalytic activity on both the Pd/C and Pd+Pt/C systems in the presence of GeO2 as well as the selectivity on the Pd+Pt/C system in the presence of GeO2. ▪Upon the selective catalytic hydrogenation of nitric acid to hydroxylamine, the promotion effect of one or more additional metals on Pd/C or Pd+Pt/C system in the presence of GeO2 has been investigated. Among various metal elements used here, iron was found to be particularly effective for improving the catalytic activity on both the Pd/C and Pd+Pt/C systems as well as the selectivity on the Pd+Pt/C system. The new iron-doped multimetallic catalyst system is a promising alternative to the currently used catalyst system due to its excellent ability to convert the nitric acid into hydroxylamine.
Keywords: Nitric acid; Selective hydrogenation; Hydroxylamine; Pd/C; Fe-doping
Interaction of silver with oxygen on sputtered pyrolytic graphite by S.H. Jeong; D.C. Lim; J.-H. Boo; S.B. Lee; H.N. Hwang; C.C. Hwang; Y.D. Kim (pp. 152-158).
For Ag nanoparticles supported by sputtered HOPG, carbonate formation was observed under highly oxidizing conditions. This result implies that Ag, O and C of the support can react together forming a new species, which does not exist on the surface of pure Ag bulk. Carbonate formation is related to the deactivation of the Ag surface in heterogeneous catalysis.▪Using core level spectra, it has been observed previously that the oxidation of silver nanoparticles deposited on sputter-damaged highly ordered pyrolytic graphite (HOPG) surfaces is very different from that taking place on surfaces composed entirely of silver. It is generally accepted that the final stage of the oxidation of silver is the formation of Ag2O/AgO. However, in the case of silver nanoparticles on HOPG, Ag2O/AgO can be further oxidized to give a species of unknown composition. In the present work it has been demonstrated that under these oxidizing conditions silver nanoparticles deposited on HOPG form silver carbonate. This implies that strong metal support interactions are responsible for the different behavior of silver nanoparticles on HOPG compared to that of silver in bulk. Carbonate formation is further suggested to be responsible for the deactivation of silver catalysts.
Keywords: Silver; Graphite; Carbonate; Oxidation; Photoelectron spectroscopy
Preparation of H5PMo10V2O40 (PMo10V2) catalyst immobilized on nitrogen-containing mesoporous carbon (N-MC) and its application to the methacrolein oxidation by Heesoo Kim; Ji Chul Jung; Dong Ryul Park; Sung-Hyeon Baeck; In Kyu Song (pp. 159-165).
By taking advantage of the overall negative charge of [PMo10V2O40]5−, the H5PMo10V2O40 (PMo10V2) catalyst was immobilized on the nitrogen-containing mesoporous carbon (N-MC) as a charge matching component. In the vapor-phase oxidation of methacrolein, the PMo10V2/N-MC catalyst (200mg on PMo10V2 basis) showed a higher conversion of methacrolein and a higher yield for methacrylic acid than the unsupported PMo10V2 catalyst (700mg on PMo10V2 basis).▪Nitrogen-containing mesoporous carbon (N-MC) with high surface area (=938m2/g) and large pore volume (0.99cm3/g) was synthesized by a templating method using SBA-15 and polypyrrole as a templating agent and a carbon precursor, respectively. The N-MC was then modified to have a positive charge, and thus, to provide sites for the immobilization of the H5PMo10V2O40 (PMo10V2) catalyst. By taking advantage of the overall negative charge of [PMo10V2O40]5−, the PMo10V2 catalyst was immobilized on the N-MC support as a charge matching component. The prepared PMo10V2/N-MC catalyst was applied to the vapor-phase oxidation of methacrolein (a model surface-type reaction). It was found that the [PMo10V2O40]5− species were finely and chemically immobilized on the N-MC support as charge matching species. In the vapor-phase oxidation of methacrolein, the PMo10V2/N-MC catalyst showed a higher conversion of methacrolein and a higher yield for methacrylic acid than the unsupported PMo10V2 catalyst. Furthermore, the PMo10V2/N-MC catalyst also showed a higher conversion of methacrolein and a higher yield for methacrylic acid than the PMo10V2/SBA-15 catalyst prepared by an impregnation method. The enhanced catalytic performance of PMo10V2/N-MC in the model surface-type reaction was due to the fine dispersion of PMo10V2 species formed via chemical immobilization.
Keywords: Heteropolyacid catalyst; Nitrogen-containing mesoporous carbon; Chemical immobilization; Methacrolein; Oxidation
Catalytic ammonia decomposition over Ru/carbon catalysts: The importance of the structure of carbon support by L. Li; Z.H. Zhu; Z.F. Yan; G.Q. Lu; L. Rintoul (pp. 166-172).
In this study, Ru catalysts supported on different carbons were used for ammonia catalytic decomposition. Ru particles are highly dispersed on carbon materials, the surface area of carbons is not a critical factor in the ammonia decomposition, and the graphitic structure of carbon supports is a key issue for high catalytic performance in the NH3 decomposition process.▪Catalytic ammonia decomposition has been of increasing interests as a means of supplying pure hydrogen for fuel cells. In this study, Ru catalysts supported on different carbons were used for catalytic ammonia decomposition. The influences of the porous and graphitic structures of carbon supports on the activities of the catalysts were examined. The catalytic activity over supported Ru catalysts is ranked as Ru/GC (graphitic carbon)>Ru/CNTs (carbon nanotube)>Ru/CB-S (carbon black)>Ru/CB-C>Ru/CMK-3≈Ru/AC. The samples are characterized by XRD, N2 adsorption, Raman spectra and H2 chemisorption. Ru particles are highly dispersed on carbon supports. The optimum range of Ru particle sizes is around 3–4nm. On the support side, the graphitic structure of the carbons is critical to the activity of the supported Ru catalyst, while the surface area of carbons is less important.
Keywords: Ammonia decomposition; Catalysts; Carbon support; Graphitic structure; Pore structure
Epoxidation of 2,5-dihydrofuran to 3,4-epoxytetrahydrofuran over Ti-MWW catalysts by Haihong Wu; Yueming Liu; Lingling Wang; Haijiao Zhang; Mingyuan He; Peng Wu (pp. 173-180).
3,4-Epoxytetrahydrofuran is produced effectively, selectively and reproducibly through the liquid-phase epoxidation of 2,5-dihydofuran with H2O2 as an oxidant in the presence of water or acetonitrile over Ti-MWW catalysts. Ti-MWW is superior to conventional titanosilicates because it is capable of suppressing the side reactions such as solvolysis of oxide and allylic reactions. ▪Liquid-phase epoxidation of 2,5-dihydrofuran (DHF, 1-oxa-3-cyclopentene) to 3,4-epoxytetrahydrofuran (ETHF) has been compared among various titanosilicate catalysts like Ti-MWW, TS-1, Ti-Beta and Ti-MOR. The effects of Ti content as well as the reaction conditions such as solvent, catalyst amount, reaction temperature and time have been studied on Ti-MWW in detail. The Ti-MWW catalyst, capable of giving a conversion >95% and an epoxide selectivity >99%, was much more active and selective than the others. The 2,5-DHF epoxidation over Ti-MWW preferred water or acetonitrile as a solvent in which the solvolysis of 3,4-ETHF and the reactions on the allylic positions of 2,5-DHF were limited to an extremely low level. The deactivation of Ti-MWW was essentially due to the deposition of heavy organic species inside pore. It turned to be reusable when subjected to the regeneration by high-temperature calcination.
Keywords: 2,5-Dihydrofuran; 3,4-Epoxytetrahydrofuran; Ti-MWW; TS-1; Liquid-phase epoxidation