Topics in Catalysis

Glow discharge plasma with different voltages (700, 1000 and 1300 V) has been applied for treatment of Ni–Co/Al2O3–ZrO2 catalyst. Physicochemical properties of the catalysts were investigated by XRD, FESEM, BET and FTIR. Based on characterization results, there was an optimum amount of voltage (1000 V) in which the most uniform morphology, highest surface area and the smallest particle size was observed. On contrary of two other catalysts, 1000 V-treated Ni–Co/Al2O3–ZrO2 catalyst showed amorphous structure for NiO which led to improved dispersion of active phase and strong metal–support interactions. In this catalyst particle size distribution was narrow and average particle size was reported to be 21.2 nm. Dry reforming of methane to syngas using synthesized Ni–Co/Al2O3–ZrO2 nanocatalysts illustrated highest catalyst reactivity in the case of 1000 V-treated Ni–Co/Al2O3–ZrO2 nanocatalyst. This catalyst exhibited 99% feed conversion while 700 and 1300 V-treated catalysts showed 91 and 95% feed conversions at 850 °C, respectively. The H2/CO ratio over 700, 1000 and 1300 V treated catalysts was 0.83, 0.98 and 0.88, respectively.

Helical mesoporous materials of the MCM-41 type with two different pore sizes were prepared by one-pot synthesis procedure using myristyl (C14) or cetyl (C16) trimethyl ammonium salts as templates. They were functionalized with the MoI2(CO)3 fragment, using a 2-aminopyridine glycidyloxypropyl derivative as anchoring ligand. TEM images showed the helical nature of the material channels. The new materials were tested as catalytic precursors in the epoxidation of cis-cyclooctene, styrene, cis-3-hexen-1-ol, trans-2-hexen-1-ol, geraniol, and R-(+)limonene, using tert-butylhydroperoxide as oxidant, and were in general moderately to highly selective towards the epoxide products. The catalytic activity of materials is higher than that of the corresponding homogeneous catalyst for epoxidation of cis-cyclooctene and styrene. The major achievement of these two catalysts, however, is the excellent product selectivity control, which in both cases reaches 100 % of the 2S,3R diastereomer in the epoxidation of trans-hex-2-en-1-ol. The catalysts were also found to be truly heterogeneous with no leaching, and stable through recycling experiments, despite losing some activity.

Lanthanum ruthenate materials with perovskite type structure can be easily synthesized with ruthenium in 4+ oxidation state. La3.5Ru4.0O13 type perovskite has been synthesized in unsupported and supported forms by using various methods. This perovskite type La3.5Ru4.0O13 phase shows high thermal stability and can therefore be used as a catalyst for high temperature applications, including those for auto-exhaust emission control. The material shows good catalytic activity for the carbon/soot oxidation in view of its possible application in diesel soot oxidation for regeneration of Diesel Particulate Filter.

In present protocol, we have a developed a mixed metallic Ag–Pd nanoparticles (NPs) supported on sugarcane bagasse ash silica through immobilization of 1-[3-(dimethylamino) propyl] -3-(3-trimethoxysilylpropyl)-1,4-diazabicyclo [2.2.2] octan-1-ium hydroxide]ionic liquid Ag-PdNPs_(DMAP-DABCO)OH_SBAsilica. Ag-PdNPs_(DMAP-TMSP-DABCO) OH_SBA silica catalytic system was prepared by the method of reduction using NaBH4 as reducing agent at controlled feed rate. Further the obtained catalytic system was used as effective catalyst for ligand free Suzuki coupling reaction in ethanol solvent system at 80 °C. Synthesized catalytic system was characterized by using SEM–EDS, FT-IR, TGA–DSC and XRD analysis. The synthesized mixed metallic Ag-PdNPs catalytic system provides better catalytic activity than mono metallic nanoparticles. It is observed that, the ionic liquid and mixed metallic nanoparticles hybrid system supported on natural waste rice husk ash silica provides better stability with high efficiency and enhances the physicochemical properties through intermolecular interactions and also consequently provides ease in recyclability up to next seven turns without loss in catalytic efficiency.

A detailed kinetic analysis of ethylene homopolymerization reactions and its copolymerization reactions with 1-hexene with a supported Ti-based Ziegler–Natta catalyst (reactions in the absence and the presence of hydrogen) shows a number of distinct kinetic features which are interpreted as a manifestation of multi-site catalysis; the catalyst contains several types of polymerization centers which differ in stability and formation rates, the molecular weight of polymers they produce, and in their response to the presence of α-olefins and hydrogen. All these effects require introduction of a special kinetic mechanism which postulates an unusually low activity of growing polymer chains containing one ethylene unit, the Ti–C2H5 group, in the ethylene insertion reaction into the Ti–C bond. This peculiarity of the Ti–C2H5 group, which is probably caused by its β-agostic stabilization, predicts two kinetic/chemical features of ethylene polymerization reactions which have not been described yet, the deuterium effect on the homopolymer structure and the activation effect of α-olefins on chain initiation. Both effects were confirmed experimentally.

The valorization of light alkanes via catalytic oxidative dehydrogenation (ODH) and selective oxidation is, with a few exemptions, still not solved. Oxide catalysts play a foremost role in these reactions. The control of the nanostructure brings new ways to tune their catalytic properties, but to date this has been little explored for alkane activation. This paper offers an overview of the applications of nanostructured oxide catalysts to oxidative activation of alkanes. Relevant examples of their unusual performance, the improvement of activity and selectivity attained by these oxides, and the new features brought by ordered mesoporous oxides, are discussed. Application of nanotechnology to oxides brings both new challenges and opportunities for catalytic applications. To make the most of it, a broad multidisciplinary approach, and bridging the lack of communication among the various research areas (electronics, materials, catalysis) involved, are needed.

Reduction of NO by NH3 over metal-promoted zeolites represents the principal reaction in the selective catalytic reduction (SCR) technology for NOx removal from Diesel engine exhausts. It has been established that addition of ammonium nitrate (AN) to the reaction mixture substantially enhances the rate of this reaction, decreasing the temperature necessary for an efficient deNOx process. Nevertheless, the nature of this effect has not been completely elucidated. To investigate the NO + AN reaction mechanism, we have used individual reactants labeled with either 15N or 18O (or both isotopes), thus obtaining an experimental background for proposing the route of the SCR accelerated by AN addition. For this study, we have used as the catalysts H-BEA and Fe/H-BEA zeolites with various Si/Al ratios and various amounts and states of the iron species.

In selective catalytic reduction (SCR) systems for diesel vehicles the injected urea solution decomposes to ammonia and isocyanic acid (HNCO), which reacts with water to another ammonia molecule and carbon dioxide over the SCR catalyst or a special urea decomposition catalyst. The second reaction step, i.e. the catalytic hydrolysis of HNCO was studied on the anatase TiO2(101) surface and Al2O3(100) surface with ab initio density functional theory (DFT) calculations using a cluster model as well as with in situ diffuse reflectance infrared Fourier transform spectra (DRIFTS) investigations and kinetic experiments. The following mechanistic pathway has been identified to be most feasible: HNCO dissociatively adsorbs on the metal oxide surface as isocyanates, which are attacked by water, thereby forming carbamic acid at the surface. In a further step this intermediate is transformed to a carbamate complex, which leads to CO2 desorption and consequently NH3 formation. The comparison between the sum of the theoretical vibrational spectra of the reaction intermediates with the in situ DRIFT spectra also strongly supports the accuracy of the second reaction pathway. This mechanism holds also for the HNCO hydrolysis over γ-Al2O3 and the reactivity compared to TiO2 was found to be consistent with the heights of the barriers in the energy diagrams. Based on these promising preliminary results a computational screening has been started in order to predict the most active metal oxides and surfaces for this reaction.