Palladium supported on bacterial biomass as a novel heterogeneous catalyst: A comparison of Pd/Al2O3 and bio-Pd in the hydrogenation of 2-pentyne

Nanoparticles of palladium supported on bacterial biomass, bio-Pd, were tested for their catalytic activity in the hydrogenation of 2-pentyne in a stirred tank reactor. The rates of reaction and the selectivity obtained using the novel materials were compared to those obtained with a conventional heterogeneous catalyst, palladium on alumina, under various reaction conditions. Under the same conditions, the initial rate of reaction over a 5 wt% bio-Pd catalyst in isopropanol was only 30% of that for a 5 wt% Pd/Al₂O₃ catalyst. However, the biomass-supported showed a high selectivity, displaying quantitative conversions of alkyne after 5 h with maximum product ratios of pentene/pentane in the range of 8–14 and cis/trans product ratios in the range of 6–14. Although the conventional 5% Pd/Al₂O₃ catalyst gave very high initial pentene/pentane and cis/trans ratios (26 and 10), these values fell rapidly over the course of the reaction and became slightly lower than those observed with bio-Pd at alkyne conversions greater than 70%. For example, at 92% alkyne conversion, the bio-Pd catalyst gave a cis/trans ratio of 2.5 and pentene/pentane ratio of 3.3, as opposed to respective values of 2.0 and 2.0 with 5% Pd/Al₂O₃. This is the first time that selectivity has been demonstrated for the bio-Pd in a multi-product reaction, thus showing promise of this material for use in catalytic syntheses where it is desirable to maximise yield of a specific component. The type of bacteria used as support in the 2-pentyne hydrogenation experiments was Desulfovibrio desulfuricans. The metal particles grow within the cell envelope, are regularly dispersed and are of uniform particle size, of ～1.7 nm as determined by chemisorption. The bio-Pd is also easily separated from the product mixture and remained active and selective when reused in a subsequent hydrogenation.     

Selective Lean NO x Reduction over Metal Oxides

The present state of knowledge of NO _x reduction under lean conditions over metal oxides is summarized in this review, with an emphasis on the reaction mechanism. Although a number of nitrogen-containing intermediates have been observed and implied, including organic nitro, nitrite, cyanide, isocyanate, and ammonia, there is yet definitive observation that confirms the relevance of these to the principal reaction pathway. Individual component in a mixed oxide catalyst can participate at different stages of the NO _x reduction reaction. The nitrogen production efficiences for different oxide based catalysts are summarized, and their relationship to the nature of the catalyst is discussed.     

Comparison of effect of ferric sulfide catalyst and nickel sulfide on coliquefaction of coal and biomass

Coliquefaction of coal and sawdust in the presence of catalysts was studied under cold hydrogen pressure from 2.04 to 4.76 MPa in the temperature range of 300–400 °C. In terms of overall conversion, yields and increment values from comparisons, investigations were made on catalysts of the sulfides of Fe, Ni and Cu and the methods of catalyst preparation. As economics of the technological process is concerned, a catalyst of ferric sulfide is preferred, apart from its advantages over the catalyst of nickel sulfides in catalytic effects under three sets of reaction conditions from our experiments. The optimal operation conditions were concluded for the preferred catalyst FeS_x.     

Potassium Stability in Soot Combustion Perovskite Catalysts

The activity for soot combustion in NO _x /O₂ and stability, under reaction conditions, of two potassium-perovskite catalysts (K/SrTiO₃ and Sr_0.8K_0.2TiO₃) and a potassium-copper perovskite catalyst (K–Cu/SrTiO₃) has been studied. In fresh catalysts, potassium is more active than copper. However copper is stable under reaction conditions while potassium-catalysts are progressively deactivated due to the loss of this metal during consecutive TPR cycles.     

Effective diffusivity and optimum apparent density of vanadia catalysts for sulfur dioxide oxidation

The effective diffusivities of air and SO₂ in four industrial vanadium pentoxide catalysts were measured at steady-state using helium as the counter diffusing gas. An improved catalyst mounting technique and diffusion cell were employed. The nonsurface component of diffusion was successfully correlated using Bruggeman's model for tortuosity. and ¯a based on pore size distribution data or calculated from specific pore volume and surface. However, it was necessary to use flow porosity in place of open porosity. Since the same pore model can be used for the catalytic oxidation So₂, non-reacting flow measurements can be employed to predict effective diffusivities under reaction conditions in this case.With models for the effective diffusivity and the kinetics of the catalytic oxidation of SO₂, an optimum apparent density of the catalyst may be determined which gives the maximum rate of reaction per unit volume of catalyst. Calculations are given for the SVD catalyst.     

Hydrolysis and oxidative decomposition of ethyl acetate in sub- and super-critical water

Hydrolysis of ethyl acetate in sub-critical (633 K, 200 bar) and super-critical water (673 K, 240 bar) has been investigated in a tubular flow reactor as a model reaction for the depolymerisation of polyesters. Super-critical reaction conditions enable approximately a 10-fold hydrolysis rate in comparison to sub-critical process. The reaction products ethanol and acetic acid are stable under these conditions. Additionally, oxidative decomposition experiments were carried out using ethyl acetate, ethanol and acetic acid as feed in the presence of air, non-catalysed as well as in the presence of a heterogeneous MnO₂–CuO/Al₂O₃ catalyst (Carulite 150^®). The catalyst caused only slight increase of ethyl acetate conversion in oxidation compared to hydrolysis, but a noticeable increase in CO₂ formation due to destruction of ethanol and acetic acid. In absence of catalyst, the degrees of conversion and selectivities were not affected by addition of oxygen. Fresh and spent catalysts were characterised with standard methods (BET, ICP), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM). The catalyst material was identified as chemically and mechanically stable under the applied reaction conditions, however, a significant sintering accompanied by a deep structural alteration and a slight reduction were observed. Additionally, the stability of reactor material regarding to corrosion was also tested.     

CoPdx oxygen reduction electrocatalysts for polymer electrolyte membrane and direct methanol fuel cells

The electrochemical activity of carbon-supported cobalt-palladium alloy electrocatalysts of various compositions have been investigated for the oxygen reduction reaction in a 5 cm² single cell polymer electrolyte membrane fuel cell. The polarization experiments have been conducted at various temperatures between 30 and 60 °C and the reduction performance compared with data from a commercial Pt catalyst under identical conditions. Investigation of the catalytic activity of the CoPd_x PEMFC system with varying composition reveals that a nominal cobalt-palladium atomic ratio of 1:3, CoPd₃, exhibits the best performance of all studied catalysts, exhibiting a catalytic activity comparable to the commercial Pt catalyst. The ORR on CoPd₃ has a low activation energy, 52 kJ/mol, and a Tafel slope of approximately 60 mV/decade, indicating that the rate-determining step is a chemical step following the first electron transfer step and may involve the breaking of the oxygen bond. The CoPd₃ catalyst also exhibits excellent chemical stability, with the open circuit cell voltage decreasing by only 3% and the observed current decreasing by only 10% at 0.8 V over 25 h. The CoPd₃ catalyst also exhibits superior tolerance to methanol crossover poisoning than Pt.     

Characterization of Pt/SiO2 Model Catalysts at UHV and Near Atmospheric Pressures

Pt/SiO₂ model catalyst samples, prepared under UHV conditions in a contiguous high pressure reactor cell surface analysis chamber, have been characterized via CO oxidation reaction kinetics under elevated pressure conditions (approaching 1 atm). Reaction kinetics are studied as a function of Pt coverage (θ _Pt = 1–10 mL), along with measurements on a Pt(110) single crystal for direct comparison. CO desorption measurements and STM measurements on Pt/SiO₂ films at T = 300 K have been obtained at various θ _Pt. Kinetic results show agreement between observations on single crystal and catalyst samples, and general agreement and correlation is obtained for site calculations across the various methods. Results demonstrate the utility of well characterized model catalyst samples in obtaining qualitative and quantitative reactivity data at elevated pressures.     

Kinetics of catalyst loss during potassium-catalysed CO2 gasification of carbon

A significant fraction of the potassium catalyst can be lost by vaporization during catalysed carbon gasification. The extent of this loss depends primarily on the reaction start-up procedure. Temperature programmed experiments show that, under inert atmospheres, both KOH and K₂CO₃ react with carbon to give a reduced form of potassium-carbon complex. The formation of this complex appears to be a prerequisite for the vaporization of potassium. The rate of vaporization at 800 °C follows a first-order expression. Under gasification conditions, only a fraction of the catalyst is in this reduced form; therefore, the rate of catalyst loss during gasification is lower than that under inert atmospheres. The effect of catalyst loss on both the initial gasification rate and the variation in rate with conversion has been determined.     

A new NOx storage-reduction electrochemical catalyst

A new NO_x storage-reduction electrochemical catalyst has been prepared from a polycrystalline Pt film deposited on 8 mol% Y₂O₃-stabilized ZrO₂ (YSZ) solid electrolyte. BaO has been added onto the Pt film by impregnation method. The NO_x storage capacity of Pt-BaO/YSZ system was investigated at 350 °C and 400 °C under lean conditions. Results have shown that the electrochemical catalyst was effective for NO_x storage. When nitric oxides are fully stored, the catalyst potential is high and reaches its maximum. On the other hand, when a part of NO and also NO₂ desorb to the gas phase, the catalyst potential remarkably drops and finally stabilizes when no more NO_x storage occurs but only the reaction of NO oxidation into NO₂. Furthermore, the investigation has clearly demonstrated that the catalyst potential variation versus temperature or chemical composition is an effective indicator for in situ following the NO_x storage-reduction process, i.e. the storage as well as the regeneration phase. The catalyst potential variations during NO_x storage process was explained in terms of oxygen coverage modifications on the Pt.     

Controlling the Sulfur Poisoning of Ag/Al2O3 Catalysts for the Hydrocarbon SCR Reaction by Using a Regenerable SOx Trap

The deactivation of a silver-based hydrocarbon selective catalytic reduction catalyst by SO_x and the subsequent regeneration under various operating conditions has been investigated. Using a sulfur trap based on a silica-supported catalyst it was found that, for a Ag/SiO₂ + Ag/Al₂O₃ combination, the negative effect of SO₂ on the n-octane-SCR reaction can be eliminated under normal operating conditions. The trap can be regenerated by hydrogen at low temperatures or at higher temperatures using a hydrocarbon reductant.     

Highly efficient procedure for the synthesis of biodiesel from soybean oil using chloroaluminate ionic liquid as catalyst

The novel efficient procedure has been developed for the synthesis of biodiesel. The chloroaluminate ionic liquid has been selected for the synthesis of biodiesel. The catalyst was very efficient for the reaction with the yield of 98.5% when the reaction was carried out under the conditions of [Et₃NH]Cl-AlCl₃ (x(AlCl₃) = 0.7), soybean oil 5 g, methanol 2.33 g, 9 h, 70 °C. Operational simplicity, low cost of the catalyst used, high yields, no saponification and reusability are the key features of this methodology.     

Dynamic Methanation of CO2 – Effect of Concentration Forcing

Investigating the effect of concentration forcing of the CO₂ methanation is not only relevant for power‐to‐gas plants but also for the study of dynamic phenomena of this reaction. In this study a Ni/Al₂O₃ catalyst is investigated under concentration forcing at industrially relevant conditions. The dynamic experiments allow an evaluation in terms of the reaction rate and enable the study of the reaction mechanism. The experiments show that no methane is formed in the CO₂‐rich part of the cycle, whereas a fast hydrogenation of carbonaceous species to methane takes place upon switching to H₂.     

Selectivity enhancement in the catalytic heterogeneous hydrogenation of limonene in supercritical carbon dioxide by an ionic liquid

Ionic liquids as coated catalysts or additives tremendously alter the selectivity pattern of the heterogeneous solid catalyst in the selective hydrogenation of limonene. The conventional monometallic ruthenium over alumina catalyst combined with an ionic liquid enables the one-pot synthesis of the intermediate p-menthene through limonene hydrogenation in supercritical carbon dioxide. Among eight screened imidazolium ILs, [C₁₀mim]NTf₂ was employed as additive, or as the coating agent of ruthenium catalyst in the reaction under supercritical conditions.The coating of the heterogeneous catalyst allows the selective production of p-menthene and increases the conversion level of limonene (>99%) compared to the conversion of limonene in the reaction carried out in the presence of an ionic liquid as an additive. Results of the catalyst recycling indicate that there is no depletion of catalyst reactivity even after four successive cycles of operation under the studied reaction conditions. Further hydrogenation of p-menthene is strongly inhibited by employing an ionic liquid. The solubility of limonene or p-menthene in an ionic liquid governs the selective hydrogenation of limonene towards p-menthene.     

Estimation of activation energies during hydrodesulfurization of middle distillates

Hydrodesulfurization (HDS) of different petroleum distillates was carried out in a batch reactor using commercial CoMo catalyst and reaction conditions similar to industrial practice. Various experiments (agitation, particle size and amount of catalyst tests) were conducted with different hydrocarbon feeds to assure the operation under kinetic regime. Reaction orders and activation energies for each feed were determined by two approaches (linear and non-linear regressions). Both kinetic parameters (n and E_A) were found to follow a direct relationship with sulfur content in the feed. Reaction orders ranged between 1.96 and 3.36 and activation energies from 21.49 to 41.96 kcal/mol, which were within the range of those reported in the literature. High values of reaction order were attributed to contributions of HDS reaction of each individual compound exhibiting very different reaction rate constants.     

OXIDATION OF GLUCOSE ON SUSPENDED PT/C: REACTION KINETICS AND ABSORPTION STUDIES

In search of a suitable model reaction system for studying hydrodynamic properties of slurry reactors under reactive conditions, the oxidation of glucose on a suspended Pt/C catalyst was investigated. In addition to homogeneous kinetic measurements, gas absorption experiments in a stirred cell with a plane interface were also carried out at 25 to 45^°C using finely powdered catalyst particles. It was found that the oxygen consumption rale followed first order kinetics only at the very beginning of the reaction. If the total amount of reacted oxygen was considerably more than that of the initial saturation value (i.e. kinetic runs repeated after some time of aeration under vigorous stirring or lengthy gas absorption experiments), the order with respect to oxygen was ½ Furthermore, the half order rate constant dropped to about ½ to ¼ of its initial value and was constant only after an amount of about 1.5 x 10^?2mol O₂/g catalyst was reacted. A new plot is also proposed which permits the simultaneous determination of the volumetric mass transfer coefficients and the rate constants for a half order reaction from gas absorption experiments at various catalyst concentrations. The rate constants and the k_La values which were obtained from completely different methods were in reasonable agreement.     

The Catalytic Baeyer–Villiger Oxidation of Cyclohexanone to ε-Caprolactone over Stibium-containing Hydrotalcite

A series of hydrotalcite-like compounds were prepared under microwave irradiation, which were used to catalyze the Baeyer–Villiger oxidation of cyclohexanone to ε-caprolactone with hydrogen peroxide as oxidant. The results show that stibium-containing hydrotalcite (Sb-HTL) has good catalytic properties in the reaction. In the Baeyer–Villiger oxidation of cyclohexanone to ε-caprolactone with H₂O₂ catalyzed by Sb-HTL, the effects of reaction time, reaction temperature, amount of catalyst and H₂O₂/cyclohexanone molar ratio are also investigated in details. It is shown the cyclohexanone conversion and ε-caprolactone selectivity can reach 79.15 and 93.84%, respectively, under the optimum reaction conditions. Furthermore, Sb-HTL can be reused for six times without obvious loss of activity and selectivity. Therefore, Sb-HTL is reusable and would be a promising catalyst for the Baeyer–Villiger oxidation using green and cheap oxidants like hydrogen peroxide instead of peroxycarboxylic acids.     

Solid-state kinetics and catalytic behavior of selective oxidation catalysts from time-resolved XAFS investigations

Time-resolved measurements are required to elucidate time-dependencies of the electronic and geometric structure of a catalyst under changing reaction conditions. Monitoring the evolution of the bulk structure of a catalyst under changing conditions reveals the solid-state kinetics of the corresponding reaction. X-ray absorption spectroscopy (XAS) permits to reveal quantitative phase composition and average valence together with the evolution of the local structure. Hence, combining time-resolved XAS with simultaneous catalysis measurements may elucidate correlations between catalytic performance, the catalyst state under reaction conditions, and its solid-state kinetics. Here, results from time-resolved in situ XAS investigations of various molybdenum-based selective oxidation catalysts are compared and discussed. Model systems (i.e. α-MoO₃, hexagonal MoO₃ supported on SBA-15, and H₄[PVMo₁₁O₄₀]) suitable to distinguish structural effects and promotion by additional metal centers have been studied under changing reaction conditions. Correlations between reduction and oxidation solid-state kinetics and catalytic performance reveal the dependence of the selectivity of the catalyst on its electronic structure. In particular the re-oxidation kinetics and the average valence under reaction conditions appear to be determined by the defect structure of the underlying catalyst bulk.     

CO oxidation over CuOx-CeO2-ZrO2 catalysts: Transient behaviour and role of copper clusters in contact with ceria

The effects of ZrO₂ content on the CO oxidation activity in a series of CuO_x/Ce_xZr_1−xO₂ (x = 0, 0.15, 0.5, 0.7 and 1) catalysts were investigated, both in the absence and in the presence of H₂, i.e. preferential CO oxidation—PROX. The investigation was performed under light-off conditions to focus the effects of transients and shut-down/start-up cycles on the performance; such phenomena are expected to affect the activity of PROX catalysts in small/delocalised fuel reformers. Evidence has been obtained for a transition from an “oxidized” towards a “reduced” state of the catalyst under the simulated PROX reaction conditions as a function of the reaction temperature, leading to different active species under the reaction conditions. Both CO oxidation activity and PROX selectivity appear to be affected by this process. IR characterisation of the surface copper species suggests an important role of reduced cerium sites in close contact with copper clusters on the CO oxidation activity at low temperatures.     

Surface chemistry of phase-pure M1 MoVTeNb oxide during operation in selective oxidation of propane to acrylic acid

The surface of a highly crystalline MoVTeNb oxide catalyst for selective oxidation of propane to acrylic acid composed of the M1 phase has been studied by infrared spectroscopy, microcalorimetry, and in situ photoelectron spectroscopy. The acid–base properties of the catalyst have been probed by NH₃ adsorption showing mainly Brønsted acidity that is weak with respect to concentration and strength of sites. Adsorption of propane on the activated catalyst reveals the presence of a high number of energetically homogeneous propane adsorption sites, which is evidenced by constant differential heat of propane adsorption q_diff,initial = 57 kJ mol^?1 until the monolayer coverage is reached that corresponds to a surface density of approximately 3 propane molecules per nm² at 313 K. The decrease of the heat to q_diff,initial = 40 kJ mol^?1 after catalysis implies that the surface is restructured under reaction conditions. The changes have been analyzed with high-pressure in situ XPS while the catalyst was working applying reaction temperatures between 323 and 693 K, different feed compositions containing 0 mol.% and 40 mol.% steam and prolonged reaction times. The catalytic performance during the XPS experiments measured by mass spectrometry is in good agreement with studies in fixed-bed reactors at atmospheric pressure demonstrating that the XPS results taken under operation show the relevant active surface state. The experiments confirm that the surface composition of the M1 phase differs significantly from the bulk implying that the catalytically active sites are no part of the M1 crystal structure and occur on all terminating planes. Acrylic acid formation correlates with surface depletion in Mo⁶⁺ and enrichment in V⁵⁺ sites. In the presence of steam in the feed, the active ensemble for acrylic acid formation appears to consist of V⁵⁺ oxo-species in close vicinity to Te⁴⁺ sites in a Te/V ratio of 1.4. The active sites are formed under propane oxidation conditions and are embedded in a thin layer enriched in V, Te, and Nb on the surface of the structural stable self-supporting M1 phase.