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Acetylene hydrogenation has been investigated on 1.8 wt.% Au(I)/SiO2 and 1.9wt.% Au(II)/SiO2 catalysts prepared by fixation of Au sol to SiO2 (Aerosil 200). The mean particle size measured by TEM is 3.7 and 6.1 nm, respectively. For the sake of comparison a 2.1 wt.% Au/TiO2 sample was prepared by deposition-precipitation (DP) technique (mean particle size of Au is 3.3 nm). Transformation of acetylene was measured at 5 K/min ramp rate with gas mixtures containing the reactants at H2/C2H2=2 and 70 ratios. The C2H2 content of the gas mixture was 0.11% (0.11 kPa C2H2). The activity sequence at 423 K was: Au/TiO2>Au(I)/SiO2≫Au(II)/SiO2. Both the partial pressure of hydrogen and the temperature significantly affect the activity (acetylene conversion) and ethylene selectivity. Above 500–550 K over-hydrogenation (ethane formation) and hydrogenolysis (methane formation) decrease the ethylene selectivity. Faster deactivation and larger amount of deposit was observed on Au/TiO2 than on Au(I)/SiO2. A reaction scheme is proposed suggesting formation of sigma bonded intermediates as sp carbon hybridises to sp2 and sp3.

Pd hydrosol was synthesized by reducing PdCl2 solution with dissolved H2 in the presence of PDDA [poly(diallyldimethylammonium chloride)] as ionic stabilizer. O2 treatment resulted in the reappearance of ligand to metal charge transfer bands of PdCl 4 2− . Repeated oxidation and hydrogen treatments caused aggregation/agglomeration of the Pd particles yielding big spherical aggregates of 30–50 nm but still keeping the size of the 5–6 nm primary particles. Aggregation was attributed to the reduction of PdCl 4 2− anion having high local densities around Pd particles surrounded by PDDA polycation. Au–Pd bimetallic hydrosols were synthesized by reduction with 2-propanol and by pulse radiolysis technique in the presence of PDDA. Both reduction modes synthesize Au core–Pd shell structures. The mode of reduction was observed to affect the particle size and the thickness of the Au core and Pd shell. At the Au rich samples the differences in the optical spectra were attributed to different dispersions of the Au–Pd particles. Au–Pd bimetallic hydrosols were adsorbed on Aerosil 200 and the supported samples were tested in gas phase hydrogenation of acetylene.

Selectivity of product formation has been tested in hydrogenation of acetylene over 0.3 wt.% Pd/α-alumina and 0.5 wt.% Pd/TiO2catalysts. Non-steady-state regime of catalyst operation was tested in pulse-flow experiments. Significant carbon poisoning appears to be a necessaryrequisite for selective formation of ethylene. The effect of hydrogen and acetylene partial pressure has been tested on the selectivity of C4products. At 273–298 K the catalysts showed 26–35% selectivity for C4 hydrocarbons and

Using different reduction conditions Pd powders have been prepared and characterized by chemisorption and TPO (Temperature Programmed Oxidation) measurements. The amount of carbon deposits introduced during preparation seems to be peculiar to the preparation procedure. The O2 consumption curves attributed to PdO formation have shown two peak minima suggesting strong differences in the accessibility of Pd particles.

Formation of carbonaceous deposits from 1,3-butadiene has been investigated over a group of Pd catalysts. Hydrogen generated in decomposition of diene at 473–523 K participates in diene hydrogenation, resulting in the formation ofn-butenes. XRD measurements have confirmed formation of dissolved carbon (PdCx) phase. DRIFT measurements over 0.06 wt.%Pd/γ-Al2O3 have revealed bands at 1575 and 1464 cm−1, suggesting formation of carboxylate structures. Selectivity of the competitive hydrogenation in 1,3-butadiene and propene mixture R(BD)/R(Pr) has been measured on “fresh” and poisoned samples. Accumulation of deposits has decreased the R(BD)/R(Pr) ratio. The results have been interpreted by transport hindrance and a greater prevalence of non-selective low coordination sites on the poisoned surface. Measurements over Pd, Cu, Pt and Rh catalysts have shown that the highn-butane selectivity over Pt and Rh is also accompanied with low R(BD)/R(Pr) values, suggesting that thermodynamic and mechanistic factors are not entirely separable.

Homologation of n-pentane and cyclopentane results in formation of benzene on Ru, Os, Re and Ir/SiO2 catalysts. Formation of benzene can be explained by the insertion of carbene into terminal vinilic carbon followed by C6-dehydrocyclization.

The effect of dispersity of Ni catalysts has been investigated in the hydrogenolysis of ethane. The kinetic order in hydrogen and the apparent activation energy are dependent on the dispersity. The experimental results reveal that the structure sensitivity of this reaction appears to a certain extent through the variation of the hydrogen order.

The self-poisoning effect of deuterium exchange reactions of C1−C6 straight chain aliphatic hydrocarbons as well as hydrogenolysis and dehydrocyclization of n-hexane in the presence of deuterium on a nickel powder catalyst has been investigated. The poisoning is enhanced with increasing carbon number. The results can be correlated to the ease of dissociative adsorption, i. e. to the formation of multiply bonded species. A tentative model is proposed to explain the “decrease” of deuterium exchange in n-hexane when the reaction is shifted towards hydrogenolysis and benzene formation. It is shown that at elevated temperatures the poisoning upon deuterium exchange is caused not only by blocking of the active sites with deposits but also by hindrance of desorption of the starting molecules in the original/exchanged form.

The reaction of 2-methylpropane has been investigated in presence of helium and hydrogen over a platinum black catalyst. The appearence of olefins in the gas phase indicates that the precursor of these unsaturated compounds adsorb ed on the surface may have some role in the self-poisoning observed during hydrogenolysis and/or isomerization.

Data on chemisorption of ethane on transition metal blacks have been correlated with hydrogenolysis activity measurements. On Pt and Pd the rupture of the C−C bond seems to be a hindered process. Desorption of methane requires larger activation on Co and Ni than on Ru, Rh or or Ir blacks.

The hydrogen sorption of carbon-supported platinum catalysts, studied by the potentiodynamic method, differs significantly from that of unsupported platinum. The difference depends on the preparation method and on the nature of the support. Possible explanations are suggested as (i) some kind of interaction between metal and support atoms during impregnation, (ii) high dispersity (amorphous structure) and (iii) hydrogen spillover onto the carbon support.