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Applied Catalysis A, General (v.315, #1-152)
Review on methods to deposit catalysts on structured surfaces by Valérie Meille (pp. 1-17).
The methods used to deposit a catalyst on structured surfaces are reviewed. Physical methods such as PVD and chemical methods (sol–gel, CVD, direct synthesis, etc.) are described. The coating of catalysts based on oxide, zeolite or carbon support is detailed on various surfaces such as silicon or steel microstructured reactors, cordierite monoliths or foams, fibres, tubes, etc.Methods used to deposit metal-on-oxide catalysts, zeolite catalysts or carbon-based catalysts on structured substrates (wall-reactors) are reviewed. Wet-procedures such as suspension or sol–gel as well as physical methods such as sputtering are explained and compared with some examples. A large range of substrates is concerned: silicon microreactors, ceramic monoliths, steel foams, etc. ▪
Keywords: Washcoating; Coating; Alumina deposition; Carbon deposition; Catalytic film; CVD; PVD; Suspension; Sol–gel; Zeolite; Structured reactor; Wall-reactor; Microreactor
Characterization and hydrodesulfurization activity of CoMo catalysts supported on boron-doped sol–gel alumina by Franck Dumeignil; Koichi Sato; Motoyasu Imamura; Nobuyuki Matsubayashi; Edmond Payen; Hiromichi Shimada (pp. 18-28).
The thiophene and dibenzothiophene (DBT) HDS activities of the B-doped catalysts were maximal for B/Al=0.04 and higher than those for an industrial reference catalyst. The 4,6-dimethyldibenzothiophene (DMDBT) HDS activities, however, were lower than that for the reference catalyst and decreased with increasing B/Al ratio. These were attributed to the strong direct desulfurization character of the B-doped catalysts. ▪A series of hydrodesulfurization (HDS) catalysts was prepared by impregnation of Co and Mo on sol–gel B–Al2O3 supports with B/Al ratios of 0, 0.02, 0.04, 0.08, 0.20, 0.32, 0.49, and 0.61. The thiophene HDS and dibenzothiophene (DBT) HDS activities were both maximal for the catalyst with B/Al=0.04, with respective values 70 and 42% higher than those for an industrial reference catalyst. These maxima in HDS activity correlated with the previously reported presence of isolated BO4 surface species. These BO4 species were responsible for a local maximum in the acidity of the B–Al2O3 supports when B/Al=0.04. In contrast, the formation of mixed oxides (A9B2 and A2B) or B2O3 that also resulted in enhanced acidity of the B–Al2O3 supports had a detrimental effect on the HDS activity.The 4,6-dimethyldibenzothiophene (4,6-DMDBT) HDS activity over the CoMo/B–Al2O3 catalysts decreased when the B/Al ratio was increased. This was attributed to the strong direct desulfurization character of the CoMo catalysts supported on the B–Al2O3 supports, because high hydrogenation ability toward the CC double bonds is essential prior to sulfur removal from 4,6-DMDBT. The excellent performance in the thiophene and DBT HDS of the CoMo/B–Al2O3 catalysts is particularly useful for ultra-deep HDS of light fractions.
Keywords: Hydrodesulfurization; Boron; Alumina; Sol–gel; Thiophene; DBT; 4,6-DMDBT; Acidity
Accessibility in alumina matrices of FCC catalysts by M. Falco; E. Morgado; N. Amadeo; U. Sedran (pp. 29-34).
A kinetic approach on the conversion of tri-isopropylbenzene at 500°C characterized accessibility in FCC resid catalyst alumina matrices with mean pore sizes between 64 and 201Å. The apparent first order kinetic constants and the conversion profiles defined a ranking of activities associated to accessibilities, that followed the same trend as the mean pore size of the aluminas. ▪The accessibility in aluminas considered to be representative of matrices used in FCC resid catalysts, with mean pore sizes between 64 and 201Å, was characterized through a kinetic approach by means of the conversion of 1,3,5-tri-isopropylbenzene (TIPB) at 500°C in a CREC Riser Simulator fluidized bed laboratory reactor. The product distribution was essentially the same as that observed on an equilibrium commercial FCC catalyst, but the activity of the aluminas was much lower. The main products (propylene, benzene, isopropylbenzene, di-isopropylbenzenes) showed that a series cracking mechanism prevailed in the conversion of TIPB. The apparent first order kinetic constants assessed and the conversion profiles allowed establishing a ranking of activities that could be associated directly to accessibilities and not to the number of acid sites (Lewis nature), which was proportional to the specific surface area of the alumina. The sequence of accessibilities followed the same trend as the mean pore size of the aluminas.
Keywords: Accessibility; Catalytic cracking; Matrix; Resid; Alumina
Effects of the H2S partial pressure on the performance of bimetallic noble-metal molybdenum catalysts in simultaneous hydrogenation and hydrodesulfurization reactions by David Pérez-MartÃnez; Sonia A. Giraldo; Aristóbulo Centeno (pp. 35-43).
Noble-metal molybdenum (NM-Mo, NM=Pt, Ru, Pd) supported on γ-Al2O3 catalysts and conventional CoMo/γ-Al2O3 were not poison by the H2S, but an inhibition of both HDS and HYD reactions was observed. This inhibition is explained by the interconversion of HDS, HYD and inactive sites. The interconversion of sites is influenced by the H2S/H2 ratio, the nature of the NM and the composition of catalysts. ▪The influence of the H2S concentration on the activity and selectivity to hydrodesulfurization (HDS) of bimetallic noble-metal molybdenum (NM–Mo, NM=Pt, Ru, Pd) supported on γ-Al2O3 catalysts was studied. The effect of H2S on the modification of the HDS pathway and the influence of the Mo loading on the sulfur resistance of catalysts were also analyzed. NM–Mo/γ-Al2O3 and conventional CoMo/γ-Al2O3 catalysts were prepared and evaluated in simultaneous dibenzothiophene (DBT) HDS and naphthalene hydrogenation (HYD) reaction cycles, in the presence of dimethyl disulfide (DMDS) in order to obtain H2S partial pressures of 10, 30 and 50kPa. Catalysts were characterized by atomic absorption spectroscopy and temperature-programmed reduction of sulfides (TPRS). TPRS experiments after exposing catalysts to simulated reaction conditions (TPRS-SRC) were also performed. Results show that the H2S does not poison the studied catalysts, but an inhibition of both HYD and HDS reactions is observed. The inhibition of catalyst activities is attributed to the interconversion of HDS, HYD and inactive sites; this interconversion is influenced by the H2S/H2 ratio, the nature of the NM and the composition of catalysts. Activity, TPRS and TPRS-SRC results confirmed this scheme. A modification of the reaction pathway was observed when the H2S partial pressure was increased; the direct desulfurization was principally affected. The interconversion of sites could explain this modification. Moreover, our results show that the Mo loading and specifically the Pt/Mo ratio, which determine the Pt dispersion, influence the sulfur resistance of the catalyst.
Keywords: Hydrotreatment; Hydrodesulfurization; Noble-metal molybdenum catalysts; H; 2; S partial pressure; TPR
Structural, morphological and acidic changes of nanocrystalline aluminas caused by a controlled humidity atmosphere by Roberto Rinaldi; Fred Y. Fujiwara; Ulf Schuchardt (pp. 44-51).
Besides the multilayer water adsorption on the alumina surface, water vapor can react with transition aluminas, yielding boehmite and bayerite microparticles. Recalcination of these transition aluminas exposed to humidity can only recover their long-range structures, however, is not effective in restoring their initial acidity. ▪The changes in the structural, morphological and acidity properties of nanocrystalline aluminas provoked by hydration under a controlled humidity atmosphere at room temperature were studied. Besides the physical and chemical adsorption of water on the surface, the hydration process causes the formation of aluminum oxy-hydroxide and trihydroxide (boehmite and bayerite). The recalcination of hydrated γ-Al2O3 cannot recuperate the initial acidic properties of the material. The populations of weak to moderate acid sites strongly decrease under recalcination of hydrated aluminas. On the other hand, the stronger acid site populations are not strongly affected by recalcination.
Keywords: Alumina; Controlled hydration
Water-soluble manganese(III) salen complex as a mild and selective catalyst for oxidation of alcohols by Bahram Bahramian; Valiollah Mirkhani; Majid Moghadam; Amir H. Amin (pp. 52-57).
Mild and efficient oxidation of alcohols with sodium periodate catalysed by water-soluble Mn(salen)OAc is reported. ▪Dicationic Mn(III) salen, containing phosphonium groups at 5,5′-positions of salen ligand, was used as an efficient and selective catalyst for oxidation of alcohols to their corresponding aldehyde or ketone derivatives at room temperature in good to excellent yields. The effect of different solvents was studied in the oxidation of 4-methoxybenzyl alcohol, CH3CN/H2O was better solvent. Also the effect of the oxygen donors such as NaIO4, Bu4NIO4, Oxone, H2O2, H2O2/urea, NaOCl and tert-BuOOH was studied in the oxidation of 4-methoxybenzyl alcohol and selected NaIO4 as oxygen donor.
Keywords: Alcohols; Aldehydes; Ketones; Oxidation; Manganese salen; Periodate
Effects of Ce addition on the Pt-Sn/γ-Al2O3 catalyst for propane dehydrogenation to propylene by Changlin Yu; Qingjie Ge; Hengyong Xu; Wenzhao Li (pp. 58-67).
Over Pt-Sn/1.1Ce-Al catalyst, the >38% of propane conversion, >98% propylene selectivity and >37% propylene yield could be kept over 50h for the reaction of propane dehydrogenation to propylene at 576°C. ▪The effects of Ce addition on the Pt-Sn/γ-Al2O3 catalysts for propane dehydrogenation to propylene have been investigated by reaction tests and some physicochemical characterizations like XRD, BET, NH3-TPD, H2-TPD, H2-TPR, H2-chemisorption, CO-FTIR and TPO. The results show that the Ce addition could greatly improve the catalytic performance and catalytic stability of the Pt-Sn/γ-Al2O3, which is reported as the optimal catalyst for propane dehydrogenation to propylene. We could keep >38% of propane conversion, >98% propylene selectivity and >37% propylene yield over 50h in the reaction of propane dehydrogenation to propylene over Pt-Sn/Ce-Al2O3 catalysts at 576°C, 3800h−1 and H2/C3H8/Ar=1/1/5. The presence of Ce in the Pt-Sn/Ce-Al2O3 catalysts could not only stabilize the active states of Pt, Sn and support, but could also suppress the coke accumulation on the catalyst during reaction, and further improve the catalytic performance of Pt-Sn/γ-Al2O3.
Keywords: Pt-Sn/γ-Al; 2; O; 3; catalyst; Ce addition; Propane dehydrogenation to propylene
Role of nickel and vanadium over USY and RE-USY coke formation by Alyne S. Escobar; Fernanda V. Pinto; Henrique S. Cerqueira; Marcelo M. Pereira (pp. 68-73).
The present paper approaches the role of nickel and vanadium oxidation state in the coke formation from cyclohexane model cracking reaction over USY and RE-USY zeolites. The coke yield increased due to the presence of Ni0, V3+ and V5+ species on USY. Rare-earth elements strongly inhibited the vanadium effect on coke formation and enhance coke formation on nickel sites. â–ªThe present paper approaches the role of nickel and vanadium oxidation states in the coke formation from cyclohexane model cracking reaction over USY and RE-USY zeolites. The coke yield increased for both zeolites, USY and RE-USY, due to the presence of nickel and/or vanadium contaminant metals. USY loaded with Ni and V presented about the same reducibility of USY loaded distinctly with Ni or V, when steam deactivation is not applied previously. However, coke formation decreased by a factor of 2 for RE-USY or USY loaded with Ni and V when compared to Ni or V loaded distinctly. This factor was affected neither by oxidation/reduction treatments, nor by rare-earths presence. After oxidation treatment vanadium is the principal responsible for coke formation. For V-USY catalyst the coke yield increase by a factor of 2.7 after reduction, while for Ni-USY catalyst coke yield increase by a factor of 13. For the RE-USY catalyst, the coke formation is strongly inhibited on vanadium sites and promoted on nickel sites. These results suggest that the coke formation on the zeolite acidic sites is influenced by multi-component interaction between Ni-V, Ni-RE and V-RE elements.
Keywords: Nickel; Vanadium; USY zeolite; Rare-earth; Coke
Oxovanadium(IV) complex of 2-(α-hydroxyethyl)benzimidazole covalently bonded to chloromethylated polystyrene for oxidation of benzoin by Mannar R. Maurya; Sweta Sikarwar; P. Manikandan (pp. 74-82).
Oxovanadium(IV) complex of 2-(α-hydroxyethyl)benzimidazole (Hebmz) have been covalently attached to chloromethylated polystyrene cross-linked with divinylbenzene and used for the oxidation of benzoin. ▪Vanadyl sulphate reacts with 2-(α-hydroxyethyl)benzimidazole covalently bonded to chloromethylated polystyrene (PS–Hhebmz) cross-linked with 5% divinyl benzene to give PS–[VO(hebmz)2]. Characterisation of the catalyst was carried out by IR, electronic and EPR spectroscopic studies, thermogravimetry, scanning electron micrographs and elemental analyses. Catalytic potential of the complex was tested for the oxidation of benzoin using tert-butyl hydroperoxide (TBHP) as an oxidant in methanol where benzil, methylbenzoate, benzoic acid and dimethylacetal were obtained as products. Various parameters such as different solvents and concentration of the substrate as well as oxidant have been taken into consideration for the maximum oxidation of the benzoin. Under optimised reaction conditions, a maximum of 98.9% conversion of the benzoin was achieved after 6h of reaction time where selectivity of the obtained reaction products varied in the order: methylbenzoate (48.5%)>benzil (19.5%)>dimethylacetal (17.1%)>benzoic acid (11.5%). Neat complex was also prepared to compare its catalytic property with polymer-anchored one. EPR spectra of neat and polymer anchored catalyst are characteristics of V(IV) complexes with typical axial pattern and possible square pyramidal geometry. The identical EPR spectral patterns of both freshly prepared and recovered anchored catalysts indicate that the complex is stable and the coordination environment is retained at the end of the catalytic reaction.
Keywords: Polystyrene; 2-(α-Hydroxyethyl)benzimidazole; Polymer-anchored complex; Vanadium(IV) complex; Oxidation of benzoin
MOCVD of iron with [(arene)(diene)Fe(0)] precursors in a fluidized bed reactor by K. Michkova; A. Schneider; H. Gerhard; N. Popovska; I. Jipa; M. Hofmann; U. Zenneck (pp. 83-90).
MOCVD of thin iron films at moderate temperature ( T<200°C) was investigated using two metal organic complexes of the type [(arene)(diene)Fe(0)] as precursor. [(1,3-Butadiene)(toluene)Fe(0)] (1) and [(1,3-cyclohexadiene)(toluene)Fe(0)] (2) were synthesized by metal vapor synthesis. They were characterized by their vapor pressure at different temperatures and their decomposition behavior.1 and2 were used to coat alumina powder with iron through MOCVD in a fluidized bed reactor (FB-MOCVD) to prepare potential supported iron metal catalysts. The new materials were compared to an iron coated sample, which was prepared by conventional wet impregnation technique. Both were characterized by different methods like ICP OES, SEM/EDX, particle size analysis, H2/TPR and CO adsorption. The iron layer of the FB-MOCVD samples forms nanocrystals, which are homogeneously distributed over the surface. They are much smaller in size and show a higher dispersion with respect to the conventionally prepared iron catalysts. As a consequence, the nanocrystals are significantly more reactive with respect to redox processes and adsorb about 40% more carbon monoxide, than the conventionally prepared material, thus indicating a higher catalytic activity.Iron is widely used as catalyst for industrial applications. Compared to other conventional techniques (wet impregnation) metal organic chemical vapor deposition in fluidized bed reactors (FB-MOCVD) have advantage of production of high dispersed metal-supported catalyst. The homogeneity of the dispersion of iron particles over alumina using new [(arene)(diene)Fe(0)] complexes as precursor was shown. These complexes may overcome the disadvantages of the commercially available compounds. ▪
Keywords: Fe/Al; 2; O; 3; catalyst; MOCVD; Wet impregnation; Fluidized bed reactor; [(1,3-Cyclohexadiene)(toluene)Fe(0)]; [(1,3-Butadiene)(toluene)Fe(0)]; TPR; CO adsorption
Tungsten-containing MCF silica as active and recyclable catalysts for liquid-phase oxidation of 1,3-butanediol to 4-hydroxy-2-butanone by Yang Su; Yong-Mei Liu; Lu-Cun Wang; Miao Chen; Yong Cao; Wei-Lin Dai; He-Yong He; Kang-Nian Fan (pp. 91-100).
W-containing mesocellular silica foams (MCF) having a Si/W (molar) ratio of 10–40 were synthesized and investigated with regard to their performance in the selective liquid-phase oxidation of 1,3-butanediol (1,3-BDO) to 4-hydroxy-2-butanone (HB). A very stable catalytic activity as a function of cycling test was observed for the as-synthesized W-MCF catalysts. ▪W-containing mesocellular silica foams (MCF) having a Si/W (molar) ratio of 10–40 were synthesized and characterized by means of N2 adsorption, SAXS, XRD, TEM, DRIFTS, DR UV–vis and Raman spectroscopy. The results show that tungsten was well incorporated inside the MCF material and the nature of WO x species closely depends on the tungsten content. At low tungsten content (Si/W≥20), the characteristic mesocellular structure of the MCF material was well maintained while at higher tungsten content (Si/W∼10) a significant degradation of the mesocellular arrangement of MCF pores was observed. The selective liquid-phase oxidation of 1,3-butanediol (1,3-BDO) to 4-hydroxy-2-butanone (HB) over the W-MCF material with various Si/W ratios was investigated. Under optimized reaction conditions, the W-MCF catalyst showed a superior catalytic performance in the selective oxidation of 1,3-BDO as compared to other W-containing materials such as WO3/MCF and W-SBA-15. Moreover, a very stable catalytic activity as a function of cycling test was observed for the W-MCF catalyst.
Keywords: Tungsten; Mesocellular silica foams (MCF); 4-Hydroxy-2-butanone (HB); 1,3-Butanediol (1,3-BDO); Hydrogen peroxide; Liquid-phase oxidation
Aromatics reduction of pyrolysis gasoline (PyGas) over HY-supported transition metal catalysts by P. Castaño; B. Pawelec; J.L.G. Fierro; J.M. Arandes; J. Bilbao (pp. 101-113).
The hydrodearomatization of pyrolysis gasoline (PyGas) over bifunctional catalysts, based on noble metals (Pt, Pd, Ir, Ni) supported on a HY zeolite, has been studied in a fixed-bed reactor. The surface structures of the catalysts were determined by CO chemisorption, photoelectron spectroscopy (XPS), temperature-programmed reduction (TPR) and temperature-programmed desorption of H2 (H2-TPD). Catalyst acidity was assessed by ammonia desorption measured by differential scanning calorimetry (DSC-NH3) and Fourier transform infrared spectroscopy of adsorbed pyridine (FTIR-Py). The kinetic performance and product selectivity of the catalysts were discussed in terms of the data provided by surface characterization techniques. Kinetic interpretation was carried out by using individual step conversion, i.e. hydrogenation and ring-opening. The results under mild ring-opening (MRO) conditions indicate a strong dependence of the hydrogenation activity on the metal used. Operating under severe ring-opening (SRO) conditions, a linear dependency of conversion and n-alkane yield on total acidity of the catalyst was observed.
Keywords: Hydrodearomatization; Ring-opening; Hydrotreatment; Pyrolysis gasoline; Transition metal bifunctional catalysts; HY zeolite
One pot selective hydrogenation and dynamic kinetic resolution over Cu/Al2O3: A way to (−)-menthol starting from low value mint oils by Nicoletta Ravasio; Federica Zaccheria; Achille Fusi; Rinaldo Psaro (pp. 114-119).
One pot selective hydrogenation of (+)-pulegone to menthols can be obtained by using a heterogeneous copper catalyst under very mild experimental conditions. Stereoselectivity to (−)-menthol can be improved from 23 to 41% by exploiting a dynamic kinetic resolution over the same catalyst in a one pot-one step process. ▪Different Cu catalysts have been used for the hydrogenation of very low value mint oils, namely, dementholized cornmint oil and Spanish pennyroyal oil.During the hydrogenation of dementholized oil Cu/Al2O3 showed the best activity and selectivity towards a mixture of menthols, while stereoselectivity toward the valuable isomer (−)-menthol can be improved by selectively dehydrogenating the products mixture.In the hydrogenation of pulegone and pennyroyal oil Cu/Al2O3 showed an unprecedented activity allowing complete transformation of the substrate into menthols under very mild experimental conditions (1atm H2, 90°C). Moreover, a dynamic kinetic resolution process taking place during the hydrogenation step, allows to enrich the mixture in (−)-menthol.
Keywords: Copper catalysts; Renewables; Essential oils; Hydrogenation; Dynamic kinetic resolution
Asymmetric epoxidation of styrene and chromenes catalysed by dimeric chiral (pyrrolidine salen)Mn(III) complexes by Dongping Wang; Mei Wang; Rong Zhang; Xiuna Wang; Aiping Gao; Jia Ma; Licheng Sun (pp. 120-127).
Two dimeric chiral (pyrrolidine salen)Mn(III) complexes3 and4 were prepared, in which the two (pyrrolidine salen)Mn(III) units are linked either by a p-xylylene or by a p-phthalyl bridge. High yields were attained for asymmetric epoxidation of styrene and substituted chromenes at 0.5–4.0mol% catalyst loading of3 and4 using NaClO/PPNO and m-CPBA/NMO as oxidant systems, with 37–39% ee for styrene and 86–95% ee for substituted chromenes. Dimeric complexes3 and4 displayed higher activities than their parent monomeric complexes1 and2 of double equiv for epoxidation of substituted chromenes. Complex3 bearing two tertiary amine units displayed considerably higher activity than analogous dimeric complex4 containing two carboxamide units in the aforementioned reaction. The effect of excess CH3I on the epoxidation of 6-nitro-2,2-dimethylchromene catalysed by3 in the aqueous/organic biphasic medium was explored. The recovery and recycling possibilities of the dimeric complexes3 and4 were studied.
Keywords: Asymmetric epoxidation; Chromene; Dimeric manganese complex; Salen ligand; Styrene
The nature of catalytic activity and deactivation of chloroaluminate ionic liquid by Anatoly S. Berenblyum; Evgeny A. Katsman; Yury Z. Karasev (pp. 128-134).
The chloroaluminate ionic liquid (CAIL) of the (CH3)3NHCl· nAlCl3 composition was studied in heptane isomerization reaction. CAIL is a typical homogeneous catalytic system containing the following: active component (HCl), co-catalyst (AlCl3) strengthening its catalytic activity, and solvent—so-called “neutral� ionic liquid. Its main deactivation causes were studied including HCl loss and poisoning by acid soluble oil (ASO) accumulation. ▪The chloroaluminate ionic liquid (CAIL) of the (CH3)3NHCl· nAlCl3 composition was studied by physico-chemical methods and catalytic activity measurements in heptane isomerization reaction. The data were also obtained on HCl solubility in CAIL depending on pressure and AlCl3 distribution between CAIL and heptanes depending on concentration. Based on obtained results CAIL is a homogeneous catalytic system containing an active component (HCl), co-catalyst (AlCl3) strengthening its catalytic activity, and solvent—so-called “neutral� ionic liquid. The CAIL main deactivation causes were studied including HCl loss and formation of acid soluble oil (ASO) poisoning the catalyst. The difference between CAIL and superacid catalysts poisoning by ASO was discussed.
Keywords: Chloroaluminate ionic liquid; Catalytic activity; Catalyst deactivation; Paraffin isomerization; Acid soluble oil (ASO)
Synthesis, structure and three way catalytic activity of Ce1− xPt x/2Rh x/2O2− δ ( x=0.01 and 0.02) nano-crystallites: Synergistic effect in bimetal ionic catalysts by Arup Gayen; Tinku Baidya; Krishanu Biswas; Sounak Roy; M.S. Hegde (pp. 135-146).
Bimetal ionic Ce1− xPt x/2Rh x/2O2− δ ( x=0.01 and 0.02) catalyst with Pt in 2+ and Rh in 3+ states is synthesized by a single step solution combustion method. The bimetal ionic catalyst induces reduction of Rh3+ at a lower temperature in presence of Pt2+ ion compared to the corresponding mono-metal ionic catalysts, Ce1− xPt xO2− δ and Ce1− xRh xO2− δ, showing enhanced catalytic activity as well as synergistic effect.▪Bimetal ionic Ce1− xPt x/2Rh x/2O2− δ ( x=0.01 and 0.02) catalysts have been synthesized by a single step solution combustion method. CO and C2H4 oxidation and NO reduction activities of the bimetal ionic catalysts are compared with mono-metal ionic Ce1− xPt xO2− δ ( x=0.01 and 0.02) and Ce1− xRh xO2− δ ( x=0.01 and 0.02) catalysts. X-ray diffraction (XRD), transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS) studies show incorporation of Pt2+ and Rh3+ ions in CeO2 lattice. Low temperature hydrogen uptake at 0°C and below over bimetal ionic catalyst shows enhanced redox property over the corresponding mono-metal ionic analogues. The TOF for CO oxidation over Ce0.99Pt0.005Rh0.005O2− δ is 0.035s−1 at 120°C, compared to 0.003s−1 over Ce0.99Pt0.01O2− δ and 0.035s−1 over Ce0.99Rh0.01O2− δ at 135°C. Enhanced catalytic activity of Ce1− xPt x/2Rh x/2O2− δ ( x=0.01) bimetal ionic catalysts compared to mono-metal ionic catalysts, Ce1− xPt xO2− δ and Ce1− xRh xO2− δ, is attributed to synergism brought about by the easy reduction of Rh3+ ion by Pt2+ ion.
Keywords: Pt–Rh synergism; Bimetal ionic catalysts; Ceria; Ionic dispersion
Friedel–Crafts-type conjugate addition of indoles using fluorapatite doped zinc bromide as efficient solid catalyst by Rachid Tahir; Klaus Banert; Saïd Sebti (pp. 147-149).
Fluorapatite doped zinc bromide was found to be a very efficient heterogeneous catalyst for the preparation of 3-substituted indoles from Michael addition of indoles to α,β-unsaturated ketones in good to excellent yields. The substitution on the indole nucleus occurred exclusively at the 3-position, and N-alkylation products have not been observed.The synthesis of 3-substituted indoles was carried out in presence of zinc bromide supported on fluorapatite. The substitution on the indole nucleus occurred exclusively at the 3-position and N-alkylation products have not been observed. Fluorapatite showed to be a very interesting macroligand for Lewis acid catalyst. ▪
Keywords: Fluorapatite; Zinc bromide; Heterogeneous catalysis; 3-Substituted indoles; Michael addition
Catalytic condensation process for the preparation of organic peroxides from tert-butyl hydroperoxide and benzylic alcohols by Aliakbar Tarlani; Abdelkhalek Riahi; Mansour Abedini; Mostafa Mohammadpour Amini; Jacques Muzart (pp. 150-152).
The selectivity depends on the nature of R1 and R2 substituents. ▪The Wells–Dawson tungsten heteropolyacid H6P2W18O62 catalyzes the formation of dissymmetric peroxides from tert-butyl hydroperoxide and various benzylic alcohols. In some cases, these catalytic conditions led to benzylic ethers as side compounds.
Keywords: Heteropolyacid; Catalysis; tert; -Butyl hydroperoxide; Benzylic alcohols; Peroxides