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Applied Catalysis A, General (v.342, #1-2)

Editorial Board (pp. co2).

Contents (pp. iii-viii).

Eric Gérard Joseph Derouane (1944–2008) by Jacques C. Védrine; Michel Che; Fernando Ramôa Ribeiro; Jianliang Xiao; Bao-Lian Su (pp. 1-2).

Dynamic methods for catalytic kinetics by Rob J. Berger; Freek Kapteijn; Jacob A. Moulijn; Guy B. Marin; Juray De Wilde; Maria Olea; De Chen; Anders Holmen; Luca Lietti; Enrico Tronconi; Yves Schuurman (pp. 3-28).

This paper reviews different transient methods amenable for determination of reaction kinetics. Transient methods allow extracting more and better kinetic information from fewer experiments compared to conventional steady-state experiments. The present day availability of experimental and analysis equipment and of more easily applicable numerical tools justifies a reappreciation of transient kinetic analysis techniques. ▪The application of various transient techniques in heterogeneous catalysis (TAP, step-response experiments, SSITKA, TEOM), with the aim to determine reaction kinetics for design purposes, is presented for several cases. These cases, comprising catalytic cracking, diffusion in zeolites, simultaneous NO_x and SO_x removal, syngas production from methane by chemical looping and selective catalytic reduction of NO_x, show that transient techniques can be well used for the purpose of rapid determination of the reaction kinetics without the laborious classical approach of steady-state kinetic measurements and without the need of high levels of sophistication to interpret and process the experimental data. In this respect transient kinetics deserve, next to fundamental catalysis studies, more frequent application in design studies for industrially relevant reaction systems. Topics and challenges for further developments in transient studies are indicated.

Keywords: Transient technique; Kinetics; Heterogeneous catalysis; TAP; SSITKA; TEOM; Step-response experiments; Isotopic Labeling; Temperature programming; Concentration programming; Catalytic cracking; Diffusion in zeolites; SCR; Methane coupling; Chemical looping; SO; _x; and NO; _x; removal

Highly porous organic–inorganic hybrid silica and its titanium silicate analogs as efficient liquid-phase oxidation catalysts by Debraj Chandra; Subhash Chandra Laha; Asim Bhaumik (pp. 29-34).

Vinyltrialkoxysilane was polymerized under non-aqueous conditions. This polymeric precursor was used for the synthesis of organic–inorganic hybrid mesoporous silica and its titanium silicate analogs. Titanium containing hybrid materials showed good catalytic activity and epoxide selectivity in the liquid-phase oxidation of R-(−)-carvone using dilute aqueous H₂O₂ as oxidant.▪Vinyltrimethoxysilane was polymerized under non-aqueous conditions through radical initiation. The resulting polymer was used as precursor in the presence of self-assembly of cationic surfactant cetyltrimethylammonium bromide (CTAB) to obtain the mesoporous organic–inorganic hybrid polyvinylsiloxane (HPVS-1). An identical synthesis procedure was followed together with the addition of different amounts of titanium(IV) source in the synthesis gels to obtain its titanium silicate analogs (Ti-HPVS-1). XRD, TEM and N₂ sorption measurements suggested highly porous wormhole-like disordered framework structures with high BET surface areas for these materials. Solid-state²⁹Si MAS NMR, UV–vis and FT IR spectroscopic tools and ICP-OES elemental analysis were used to characterize these materials. Spectroscopic results suggested the incorporation of isolated tetrahedral Ti(IV) sites in the organically modified hybrid silica frameworks. Ti-HPVS-1 showed excellent catalytic activity and high selectivity in the liquid-phase oxidation of R-(−)-carvone to the corresponding epoxide, using dilute aqueous H₂O₂ as oxidant.

Keywords: Mesoporous materials; Organic–inorganic hybrid; Titanium silicate; Epoxidation

Supported ruthenium catalysts for selective methanation of carbon oxides at very low CO_x/H₂ ratios by Zbigniew Kowalczyk; Kazimierz Stołecki; Wioletta Raróg-Pilecka; Elżbieta Miśkiewicz; Ewa Wilczkowska; Zbigniew Karpiński (pp. 35-39).

A group of supported ruthenium catalysts was characterized (O₂, CO chemisorption) and tested in methanation of small CO_x amounts (1000–5000ppm) in H₂-rich streams. The surface-based reaction rates (TOF) of methanation proved to be dependent on the kind of support material (graphitized carbon, alumina, magnesia and Mg–Al spinel) and metal dispersion. For high Ru dispersions (0.73–0.8) the following sequence of TOFs was obtained: Ru/Al₂O₃>Ru/Mg–Al>Ru/MgO>Ru/C both for CO and CO₂ hydrogenation. The 15%Ru/Al₂O₃ system was found to be significantly more active than the commercial Ni-based catalyst.▪A group of supported ruthenium catalysts was prepared and tested in methanation of small CO_x amounts (1000–5000ppm) in hydrogen-rich streams. Low (66m²/g) and high (440m²/g) surface area graphitized carbons and three oxide materials: magnesia (94m²/g), alumina (225m²/g) and an Mg–Al spinel (96m²/g) were used as supports for the metal and ruthenium carbonyl was used as the Ru precursor. The catalysts were characterized by the chemisorption technique, using O₂ and CO as adsorbates. The studies of CO_x methanation (flow reactor, atmospheric pressure) have shown that some of the supported ruthenium catalysts exhibit high activities referred to the metal mass. The catalytic properties of ruthenium surfaces expressed by TOFs proved to be dependent on the kind of support material and metal dispersion. In general, the surface-based reaction rates are the higher, the lower the Ru dispersion (fraction exposed FE), which suggests a dominant role of ensembles of contiguous surface planar Ru atoms. For high metal dispersions (FE=0.73–0.8), the following sequence of TOFs was obtained: Ru/Al₂O₃>Ru/MgAl₂O₄>Ru/MgO>Ru/C, both for CO and CO₂ hydrogenation. The highly loaded alumina-based system (Ru15/Al₂O₃) proved to be significantly more active than the commercial nickel-based catalyst, both in terms of TOFs and reaction rates referred to the metal mass.

Keywords: Carbon oxides methanation; Ruthenium catalysts; Ruthenium dispersion; Carbon; Magnesia; Alumina; Mg–Al spinel support

Selective synthesis of p-cresol by methylation of phenol by M.E. Sad; C.L. Padró; C.R. Apesteguía (pp. 40-48).

The selective synthesis of p-cresol by gas-phase alkylation of phenol with methanol was studied on SiO₂–Al₂O₃ and zeolites HBEA, HZSM5 and HMCM22. The p-cresol yield and the para-/ ortho-cresol ratio on HMCM22 for 93% phenol conversion were about 58% and 3.4, respectively, the highest values reported up to now for the p-cresol formation from methylation of phenol.▪The selective synthesis of p-cresol by gas-phase alkylation of phenol with methanol was studied on SiO₂–Al₂O₃ and zeolites HBEA, HZSM5 and HMCM22. Cresols were formed from phenol alkylation of methanol via two parallel pathways: the direct C-alkylation of phenol and the conversion of anisole intermediate obtained by O-alkylation of phenol. Methylation of o- and p-cresol led to the formation of 2,6- and 2,4-xylenols while anisole produced methylanisoles either by alkylation with methanol or by disproportionation. Regarding the cresol isomers distribution, p- and o-cresol were the major products on all the samples while m-cresol formation remained always lower than 6%. SiO₂–Al₂O₃, HBEA and HZSM5 exhibited similar initial p-cresol: o-cresol ratios, between 0.6 and 0.8. In contrast, p-cresol was the predominant product on HMCM22 because the narrow sinusoidal 10-membered ring channels of this zeolite were particularly suitable for improving by shape selectivity the formation of p-cresol. Thus, we report here that p-cresol yields of 55% and p-cresol: o-cresol ratios of 4 are obtained on HMCM22 by gas-phase alkylation of phenol with methanol at 473K, atmospheric pressure and contact time of 350gh/mol phenol.

Keywords: p; -Cresol synthesis; Fine chemicals; Zeolite HMCM22; Phenol methylation

Effect of anodic polarization on carbon deposition on Ni/YSZ anodes exposed to methane by Vanesa Alzate-Restrepo; Josephine M. Hill (pp. 49-55).

The carbon formed under operating conditions was examined by investigating the effects of current density, time, and anode thickness on both the amount and type of carbon formed at 1073K. Carbon deposited under operating conditions is more reactive than the carbon formed at open circuit conditions. Increasing the current density reduces carbon formation.▪The formation of carbon is a problem when operating solid-oxide fuel cells (SOFC) containing nickel/yttria-stabilized zirconia (Ni/YSZ) anodes with hydrocarbon fuels directly. Previous studies have examined the carbon formed ex-situ on Ni/YSZ anodes. In this study, we have examined the carbon formed in-situ under operating conditions, and investigated the effects of current density, time, and anode thickness on both the amount and type of carbon formed at 1073K using temperature programmed oxidation and scanning electron microscopy. The carbon formed under operating conditions was more reactive and contained hydrogen compared to the carbon formed at open circuit potential that did not contain hydrogen. When the current density was increased less carbon was deposited, but the characteristics of the carbon did not change. With increasing time and/or anode thickness, the carbon deposits became more difficult to remove and decreased in hydrogen content.

Keywords: SOFC; Ni/YSZ; Carbon deposition; TPO; SEM

Structure and properties of bifunctional catalysts based on zirconia modified by tungsten oxide obtained by polymeric precursor method by Anne M. Garrido Pedrosa; Marcelo J.B. Souza; Bojan A. Marinkovic; Dulce M.A. Melo; Antonio S. Araujo (pp. 56-62).

Bifunctional catalysts of Pt/WO_x–ZrO₂ (PWZ) type with 1wt% of Pt and 10, 15 and 20wt% of tungsten were synthesized by polymeric precursor calcined at 600, 700 and 800°C and characterized by several techniques. Such catalysts were active in the n-heptane isomerization with high selectivity to branched product.▪Bifunctional catalysts of Pt/WO_x–ZrO₂ (PWZ) type with 1wt% of Pt and 10, 15 and 20wt% of tungsten were synthesized by polymeric precursor method and after they were calcined at 600, 700 and 800°C. The structural and textural properties of the catalysts were by X-ray diffraction (XRD), Fourier-transformed infrared spectroscopy (FTIR), N₂ adsorption measurement, temperature programmed reduction by derivative thermogravimetry (TPR–DTG) and transmission electron microscopy (TEM). X-ray diffractogram revealed the presence of tetragonal ZrO₂ and platinum (Pt) as the main phases. The infrared spectra of the catalysts showed bands due O–W–O and WO bonds. The catalysts showed specific surface area values in the range of 30–160m²g⁻¹. TPR profile showed reduction peaks at high temperatures that were related with the reduction of WO_x species. Such catalysts were active in the n-heptane isomerization with high selectivity to branched product.

Keywords: Synthesis; Zirconia; Tungsten oxide; n; -Heptane isomerization

PdZnAl catalysts for the reactions of water-gas-shift, methanol steam reforming, and reverse-water-gas-shift by R.A. Dagle; A. Platon; D.R. Palo; A.K. Datye; J.M. Vohs; Y. Wang (pp. 63-68).

PdZn catalysts have been studied for WGS reaction. Although PdZn alloys are active WGS catalysts, WGS is not involved in methanol steam reforming. RWGS reaction could be one of the sources for small amount of CO formation in methanol steam reforming.▪Pd/ZnO/Al₂O₃ catalysts were studied for water-gas-shift (WGS), methanol steam reforming, and reverse-water-gas-shift (RWGS) reactions. WGS activity was found to be dependent on the Pd:Zn ratio with a maximum activity obtained at approximately 0.50, which was comparable to that of a commercial Pt-based catalyst. The catalyst stability was demonstrated for 100h time-on-stream at a temperature of 360°C without evidence of metal sintering. WGS reaction rates were approximately 1st order with respect to CO concentration, and kinetic parameters were determined to be E_a=58.3kJmol⁻¹ and k₀=6.1×10⁷mol⁻¹. During methanol steam reforming, the CO selectivities were observed to be lower than the calculated equilibrium values over a range of temperatures and steam/carbon ratios studied while the reaction rate constants were approximately of the same magnitude for both WGS and methanol steam reforming. These results indicate that although Pd/ZnO/Al₂O₃ are active WGS catalysts, WGS is not involved in methanol steam reforming. RWGS rate constants are on the order of about 20 times lower than that of methanol steam reforming, suggesting that RWGS reaction could be one of the sources for small amount of CO formation in methanol steam reforming.

Keywords: PdZnAl catalyst; Water-gas-shift (WGS); Methanol steam reforming; Reverse-water-gas-shift; Fuel processing

Effect of temperature, steam-to-carbon ratio, and alkali metal additives on improving the sulfur tolerance of a Rh/La–Al₂O₃ catalyst reforming gasoline for fuel cell applications by Magali Ferrandon; Jennifer Mawdsley; Theodore Krause (pp. 69-77).

Complete recovery of the initial autothermal reforming activity of a Rh/La–Al₂O₃ could be achieved when switching from 34-ppm S-gasoline to S-free gasoline at 800°C, while only 50% of the activity could be recovered at 700°C. The beneficial effect of temperature, steam, and alkali metal was attributed to the inhibition of coke, which was the major cause of catalyst deactivation.▪2wt% Rh/La–Al₂O₃ was tested for autothermal reforming (ATR) of S-free and 34ppm-S-gasoline and characterized by scanning electron microscopy, elemental analyses, surface area, CO chemisorption, DRIFTS and X-ray absorption spectroscopy. The poisoning effect of S was more pronounced during ATR at 700°C than at 800°C. Complete recovery of the initial activity could be achieved when switching from S-containing gasoline to S-free gasoline at 800°C, while only 50% of the activity could be recovered at 700°C. Sulfur increased Rh sintering due to an increase in the catalyst temperature caused by a greater inhibition of steam reforming than partial oxidation. An increase in the H₂O:C from 2.0 to 3.0, or the addition of K to Rh significantly enhanced the sulfur tolerance of the catalysts. The beneficial effect of temperature, steam, and alkali metal was attributed to the inhibition of coke, which was the major cause of catalyst deactivation.

Keywords: Rh; Reforming; Gasoline; Sulfur; Poisoning; Deactivation; Coke; SEM

Improved NOx reduction over the staged Ag/Al₂O₃ catalyst system by Jong H. Lee; Steven J. Schmieg; Se H. Oh (pp. 78-86).

The reaction mechanism of reducing NOx with hydrocarbons over Ag/Al₂O₃ has been examined to improve its NOx reduction performance at lower temperatures, using ethanol and n-octane as representative hydrocarbon reductants. Based on the results obtained at the early stages of the hydrocarbon oxidation and NO reduction, it is proposed that the partial oxidation of hydrocarbons and the oxidation of NO are the first reaction steps over Ag/Al₂O₃. n-Octane is broken up into smaller hydrocarbon molecules, which are then subsequently oxidized to form various aldehydes, while ethanol is also rapidly converted to acetaldehyde. At the same time, NO is oxidized effectively to NO₂ in the presence of reductants.These observations and additional experiments with variable amounts of Al₂O₃ placed downstream of the Ag/Al₂O₃ catalyst suggest that the NO reduction by hydrocarbons over Ag/Al₂O₃ may occur via a bifunctional reaction mechanism; NO and hydrocarbons are converted into NO₂ and more reactive hydrocarbon species (i.e., smaller alkenes, oxygenated hydrocarbons), respectively, over the Ag sites, while N₂ is produced from the subsequent reactions between these intermediate species over different sites including Al₂O₃.The proposed bifunctional reaction mechanism offers an opportunity to improve the overall NOx reduction performance of Ag/Al₂O₃ by optimizing individual reaction steps separately. Thus, the concept of a staged catalyst system has been examined using Ag/Al₂O₃ for the formation of reaction intermediates, and a secondary catalyst (e.g., Al₂O₃ or BaY) for the subsequent N₂ production reaction. Significant improvement in NOx reduction to N₂ was obtained at lower temperatures, when BaY was used as the second catalyst and ethanol was used as reductant.Based on the proposed bifunctional reaction mechanism, the concept of a staged catalyst system has been examined using Ag/Al₂O₃ for oxidizing NO and hydrocarbons, and a secondary catalyst for reducing NOx with partially oxidized hydrocarbons. Significant improvement in NOx reduction to N₂ was obtained at lower temperatures, when BaY was used in the second layer and ethanol was used as the reductant. ▪

Keywords: NOx reduction; HC-SCR; Ag/Al; ₂; O; ₃; catalyst; Ethanol; n; -Octane

Kinetics of the catalytic combustion of diesel soot with MoO₃/Al₂O₃ catalyst from thermogravimetric analyses by Fábio S. Toniolo; Elisa Barbosa-Coutinho; Marcio Schwaab; Isabela C.L. Leocadio; Ricardo S. Aderne; Martin Schmal; José Carlos Pinto (pp. 87-92).

Catalytic combustion of diesel soot was performed over a molybdenum catalyst in a thermogravimetric analysis (TGA) experiment. Based on a first-order kinetic model, kinetic parameters were estimated for several experimental conditions, providing a suitable adjustment of the available experimental data. The analysis of the estimates of parameters shows that the so-called compensation effect is a mere consequence of parameter correlation, which can be easily removed through reparameterization of the Arrhenius equation. Finally, it is shown that thermogravimetric analysis, with simultaneous parameter estimation, can improve the statistical significance of the obtained results and lead to better understanding of the analyzed process.▪Catalytic combustion of diesel soot was performed over a 15-wt.% MoO₃/Al₂O₃ catalyst in a thermogravimetric analysis (TGA) system, at distinct heating rates and particulate concentrations. Kinetic parameters were then estimated for several experimental conditions, based on a first-order kinetic model and on the numerical integration of the differential mass balance equations. The estimated values of activation energies lie between 139 and 163kJ/mol, in accordance with published data for similar systems. The analysis of the parameter estimates shows that the so-called compensation effect is a mere consequence of parameter correlation, which can be easily removed through reparameterization of the Arrhenius equation. Finally, it is shown that the proposed kinetic model provides suitable fits for the available experimental data. Besides, it is shown that thermogravimetric analysis, with simultaneous parameter estimation, can improve the statistical significance of the obtained results and lead to better understanding of the analyzed process.

Keywords: Diesel soot; Thermogravimetric analysis (TGA); Kinetic modeling; Parameter estimation; Experimental design; Compensation effect

Oxidative dehydrogenation of propane on Mg-V-Al mixed oxides by S. Blanco; S.R.G. Carrazán; V. Rives (pp. 93-98).

Vanadium-magnesium mixed oxides have been prepared by thermal decomposition of decavanadate-intercalated Mg, Al LDHs and by impregnation of MgO or without Al₂O₃ with a decavanadate solution, and they have tested for ODH of propane. The differences observed for the catalytic behaviour are mainly related to their acid properties, increased by Al³⁺ decreasing the selectivity to propene.▪Vanadium-magnesium mixed oxides have been prepared by thermal decomposition of decavanadate-intercalated Mg, Al layered double hydroxides (LDHs), MgAlVO-LDH, and by impregnation of MgO (mixed, MgAlVO-I, or not, MgVO-I, with Al₂O₃) with an aqueous decavanadate solution. The activity of catalyst MgAlVO-LDH in oxidative dehydrogenation of propane is higher than that measured for the mixed oxides obtained by conventional impregnation. However, the largest normalised conversion measured over sample MgAlVO-I is assigned to the higher surface density of V centers, which are stabilised along the reaction runs. Normalised selectivity and conversion profiles show that propene is first formed and then oxidized to CO on catalyst MgAlVO-I, a process favoured by the high acidity of this solid. However, catalyst MgVO-I, with a medium strength surface acidity, is rapidly deactivated, forming CO₂, by coke deposition on exposed V sites. The low selectivity to propene of catalyst MgAlVO-LDH is related to its low surface density of V sites.

Keywords: Layered double hydroxides (LDHs); Oxidative dehydrogenation (ODH) of propane to propene; Mg-V mixed oxides

Oxidative dehydrogenation of ethane over vanadium supported on mesoporous materials of M41S family by L. Čapek; J. Adam; T. Grygar; R. Bulánek; L. Vradman; G. Košová-Kučerová; P. Čičmanec; P. Knotek (pp. 99-106).

Oxidative dehydrogenation (ODH) of ethane has been investigated over V-HMS, V-MCM-41 and V-SBA-15 catalysts. The objectives were to determine possible activity of vanadium oxo-species supported on mesoporous materials of M41S family in ODH of ethane, optimize reaction conditions and to contribute to the understanding of the relationship between the activity of vanadium species and its distribution.▪The contribution deals with mesoporous materials of M41S family post-synthetically dopped with vanadium oxo-species. The performance of V-HMS, V-MCM-41 and V-SBA-15 catalysts with varying vanadium loadings was studied in oxidative dehydrogenation (ODH) of ethane. The objectives of this study were to determine a possible activity of vanadium species supported on mesoporous materials of M41S family and to optimize reaction conditions. We contribute to the understanding of the relationship between the activity of vanadium species in ODH of ethane and its distribution. Vanadium-based catalysts were analyzed by UV–vis spectroscopy, voltammetry of microparticles (VMP), and nitrogen adsorption (determination of specific surface area). The most active catalysts contained 2–4.5wt.% V finely dispersed over mesoporous support in the form of isolated monomeric and oligomeric vanadium species. V-HMS, V-MCM-41 and V-SBA-15 exhibited comparable activity in ODH of ethane.

Keywords: Oxidative dehydrogenation; Ethane; Vanadium; Mesoporous materials

Characterization of mesoporous catalyst supports on microreactor walls by Sho Kataoka; Akira Endo; Atsuhiro Harada; Yuki Inagi; Takao Ohmori (pp. 107-112).

We fabricated and characterized mesoporous silica thin films on microreactor walls in order to perform more efficient heterogeneous catalytic reactions by using the mesoporous silica as a catalyst support. The structures of the films formed on the microreactor walls were characterized by comparing them with those of films formed on planar substrates under various conditions. Cross-section observations revealed that 120nm thick SBA-16 films with a 3D cubic structure were uniformly coated across the microreactor. Furthermore, the microreactor was employed for a heterogeneous catalytic reaction in an organic solvent to determine its suitability. An aluminum-doped SBA-16 film was formed in the same manner inside the microreactor as a catalyst, although pure SBA-16 has little catalytic activity. The results of a cyanosilylation reaction showed that the reaction rate varied with the reactant flow rate. The specific characteristics are also discussed using a mathematical model of the mass transfer inside microreactors.We fabricated and characterized mesoporous silica thin films on microreactor walls for use as a catalyst support. As a model catalyst, Al-doped mesoporous silica was employed for a cyanosilylation reaction to reveal the usability of the mesoporous catalyst support inside microreactors.▪

Keywords: Mesoporous silica; 3D cubic structure; Microreactors; Catalyst support; Cyanosilylation

Preparation, thermal stability, and CO oxidation activity of highly loaded Au/titania-coated silica aerogel catalysts by Yutaka Tai; Koji Tajiri (pp. 113-118).

Au/titania-coated silica aerogel catalysts having Au loadings ranging from 0.14 to 20wt.% have been prepared using liquid phase adsorption. In contrast to the catalysts prepared through conventional deposition–precipitation, the CO oxidation activity per catalyst increased monotonously with increasing Au loading. The diameters of the Au particles remained well below 5mm, even after calcination at 973K for 2h. ▪We have prepared Au/titania-coated silica aerogel catalysts having Au loadings ranging from 0.14 to 20wt.% using the liquid phase adsorption of preformed Au nanoparticles (NPs) onto the support. Using transmission electron microscopy, we confirmed that AuNPs as small as 2nm were well dispersed in the catalyst samples, preserving their original diameters after heat treatment at 673K. As a result, in contrast to the behavior of catalysts prepared using the conventional deposition–precipitation method, the CO oxidation activity per catalyst increased monotonously with increasing Au loading. These results suggest that this preparation procedure and support allow the AuNPs to preserve their intrinsic oxidation activities over a wide loading range. We also found that the AuNPs on this support were resistant to thermal sintering: the diameter of the particles remained well below 5nm even after calcination at 973K for 2h.

Keywords: Supported gold catalyst; Au nanoparticle; Aerogel support; Adsorption; High loadings; CO oxidation; TEM

Stability, reutilization, and scalability of activated hydrotalcites in aldol condensation by Sònia Abelló; D. Vijaya-Shankar; Javier Pérez-Ramírez (pp. 119-125).

Meixnerite (rehydrated Mg-Al hydrotalcite) is more active and selective than NaOH solutions in the citral–acetone condensation to pseudoionone, and the heterogeneous process is scalable. However, the fast poisoning of the active Brønsted basic centers upon contact with air, coupled to its limited reutilization and time-consuming regenerability represent serious drawbacks for industrial implementation of these solid bases. The lack of stringent environmental regulations further elevates the conservatism to use alkaline solutions. ▪A number of studies have shown that solid bases, among others activated hydrotalcites, are highly efficient catalysts for C–C bond formation reactions. A widely studied case is the aldol condensation of citral and acetone, where rehydrated Mg-Al hydrotalcite shows higher yields to pseudoionone compared to NaOH solutions. Despite this fact, the fine chemical industry still operates with the traditional liquid inorganic bases. This manuscript addresses technical aspects that can explain the limited implementation of activated hydrotalcites in aldol condensations. For this purpose, the catalyst stability in air, its reusability and regenerability after reaction, and the process scalability were investigated. The conciliation of activity data of the fresh hydrotalcite in batch laboratory (ml) and bench (l) reactors with on line ATR analysis is excellent, revealing that the citral–acetone reaction over hydrotalcite can be upscaled. However, the poisoning of the active Brønsted basic centers in the rehydrated hydrotalcite by CO₂ is very fast (50% activity loss after 1h exposure to ambient). Besides, the catalyst after one run is inactive due to the presence of strongly adsorbed products and requires time-consuming (and not fully complete) regeneration. Basic centers of Lewis nature in calcined hydrotalcites (basically MgO) are more stable, but their activity is very low compared to the rehydrated counterpart. Both the technical disadvantages of current solid bases and the lack of stringent environmental regulations motivate the conservatism of industry to use alkaline solutions.

Keywords: C–C bond formation; Solid bases; Aldol condensation; Hydrotalcite; Deactivation; Reutilization; Regeneration; CO; ₂; poisoning; Scale-up

Synthesis of molybdovanadophosphoric heteropoly acid solutions having modified composition by V.F. Odyakov; E.G. Zhizhina; R.I. Maksimovskaya (pp. 126-130).

Homogeneous oxidation catalysts containing modified solutions of high-vanadium heteropoly acidsHaPzMoyVx′Ob can be synthesized via successive operations A and B.▪A new practically wasteless method of synthesis of high-vanadium Mo–V–phosphoric heteropoly acids aqueous solutions having modified compositionHaPzMoyVx′Ob (HPA-x′zP) has been developed. These solutions are used as thermally stable catalysts of oxidation of organic compounds with O₂. At the first stage of the synthesis, V₂O₅ is dissolved in the cooled H₂O₂ to form peroxy vanadium compounds, which spontaneously decompose to yield H₆V₁₀O₂₈ solution. The latter is stabilized by addition of an excess of H₃PO₄. The prepared (H₉PV₁₄O₄₂+H₃PO₄) solution is added to a gradually evaporating suspension of (MoO₃+H₃PO₄) to form theHPA-x′zP solution. The catalysts based onHPA-x′zP solutions do not yield V-containing deposits up to 170°C. Syntheses ofHPA-x′zP solutions can be realized both in a lab and pilot scale.

Keywords: Mo–V–phosphoric heteropoly acids; Synthesis; Homogeneous catalysts

Homogeneous catalytic hydrogenolysis of chlorodifluoromethane by Ottó Balázs Simon; Attila Sisak (pp. 131-136).

CHF₂Cl has been converted to CHF₃ and CH₄ as main products when hydrogenolyzed in the presence of RhCl₃(py)₃ and other homogeneous catalysts modified with bases (amines and fluoride ion). Pyridine additive was partly hydrogenated and then alkylated to N-alkylpiperidines. Nucleophilic attack of fluoride ion on the substrate as well as difluorocarbene formation and hydrogenolysis in the coordination sphere of rhodium are the possible crucial steps leading to the gaseous products. ▪CHF₂Cl has been converted to CHF₃ and CH₄ as main products when hydrogenolyzed in the presence of RhCl₃(py)₃ and other homogeneous catalysts modified with bases (amines and fluoride ion). Pyridine additive was partly hydrogenated and then alkylated to N-alkylpiperidines. Nucleophilic attack of fluoride ion on the substrate as well as difluorocarbene formation and hydrogenolysis in the coordination sphere of rhodium are the possible crucial steps leading to the gaseous products.

Keywords: Chlorodifluoromethane; Hydrogenolysis; Rhodium; Trifluoromethane; Difluorocarbene

Catalytic trifluoromethylation of uracil to 5-trifluoromethyluracil by use of CF₃I and its industrial applications by Daisuke Uraguchi; Kyoko Yamamoto; Yuhki Ohtsuka; Kenji Tokuhisa; Tetsu Yamakawa (pp. 137-143).

The catalytic trifluoromethylation of uracil using CF₃I was investigated to find a new industrial process for the production of 5-trifluoromethyluracil. The catalytic system of FeSO₄, H₂O₂ and H₂SO₄ in dimethylsulfoxide efficiently and selectively yielded 5-trifluoromethyluracil under mild conditions. FeSO₄ exhibited the highest activity among the Fe(II) compounds tested. H₂O₂ was indispensable for the reaction and only Fe(II) compounds yielded the desired product. This characteristic of the reaction suggests that it proceeds in a Fenton oxidation manner. The reaction was applicable to large-scale production: 50kg of 5-trifluoromethyluracil in a 600L reactor. By the use of this catalytic system, selective trifluoromethylation at the 5-position was also performed with various uracil derivatives including uridines. Interestingly, Cp₂Fe was superior to FeSO₄ for several substrates.A catalytic system of FeSO₄, H₂O₂ and H₂SO₄ in DMSO efficiently and selectively led to the formation of 5-trifluoromethyluracil from uracil and CF₃I under mild conditions (at 40–50°C for 40–120min). This reaction could be applied to large-scale production: 50kg of 5-trifluoromethyluracil. By the use of this catalyst system, the trifluoromethylation of various uracil derivatives including uridines was also performed at the 5-position selectively.▪

Keywords: Trifluoromethylation; Trifluoromethyl iodide; Fe(II) catalyst; 5-Trifluoromethyluracil

Oxygen exchange mechanism between isotopic CO₂ and Pt/CeO₂ by A. Bueno-López; K. Krishna; M. Makkee (pp. 144-149).

The oxygen exchange mechanism between C¹⁸O₂ and CeO₂ has been studied between 200 and 600°C in a TAP reactor. Temperature above 300°C is required for the exchange of both oxygen atoms of C¹⁸O₂ with CeO₂, and only one oxygen atom is exchanged at lower temperature. Pt accelerates the exchange rate between 200 and 400°C, presenting minor effect above 400°C.▪The oxygen exchange mechanism between C¹⁸O₂ and CeO₂ and the role of Pt in this process have been studied in an advanced TAP reactor in the 200–600°C temperature range. For bare and Pt-containing CeO₂, the exchange of the oxygen atoms of C¹⁸O₂ takes place in the whole temperatures range studied, and the oxygen exchange rate increases with temperature. The proposed mechanistic pathway consists of the exchange of the oxygen atoms in the C¹⁸O₂ molecule in two consecutive steps. In the case of bare CeO₂, only one of the oxygen atoms of C¹⁸O₂ is exchanged between 200 and 300°C, and temperatures above 300°C are required for the exchange of the second oxygen atom of the C¹⁸O₂ molecule. Pt accelerates the exchange rate between 200 and 400°C, mainly favouring the exchange of the second oxygen atom of the C¹⁸O₂ molecule. The effect of Pt cannot be resolved at higher temperature (above 400°C), since at high temperature the direct exchange over bare CeO₂ is already fast.

Keywords: Cerium oxide; Carbon dioxide; Isotopic oxygen exchange; TAP; Isotope

Original carbon-based honeycomb monoliths as support of Cu or Mn catalysts for low-temperature SCR of NO: Effects of preparation variables by Mohamed Ouzzine; Gustavo A. Cifredo; José M. Gatica; Sanae Harti; Tarik Chafik; Hilario Vidal (pp. 150-158).

A series of catalysts consisting in Cu or Mn supported on lab-scale carbon-based honeycomb monoliths, which have been previously prepared following an original methodology, have been investigated in the low-temperature selective catalytic reduction of NO with NH₃. Complementary techniques employed for the characterisation have revealed significant differences between the catalysts depending on their preparative procedure.▪A series of catalysts consisting in Cu or Mn supported on lab-scale carbon-based honeycomb monoliths, which have been previously prepared following an original methodology, have been investigated in the low-temperature selective catalytic reduction of NO with NH₃. Special attention has been paid to the effect of changing different preparative variables for the incorporation of the active phase: way of introducing the metal, concentration of the precursor solution and time of contact with the monoliths in the case of impregnation, use or not of a chemical pre-treatment of the support, and the final drying procedure. Complementary techniques employed for the chemical, textural and structural characterisation have revealed significant differences between the catalysts depending on their preparative procedure.

Keywords: Carbon monoliths; Preparation method; NO abatement; SCR with NH; ₃; Copper catalysts

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Applied Catalysis A, General (v.342, #1-2)

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Applied Catalysis A, General (v.342, #1-2)