Ethane Hydrogenolysis Reaction Research Articles

O2 plasma activation of dendrimer-derived Pt/γ-Al2O3 catalysts

Platinum particles, approximately 1.6nm in size, were formed on γ-Al2O3 following impregnation with a Pt40-dendrimer precursor solution. These Pt particles are not catalytically active, since they are covered by the dendrimer component. Treatment in O2 plasma at room temperature removes the dendrimer without affecting metal dispersion. Subsequent treatment in H2 at 300°C leads to partial aggregation of Pt, although the degree of such aggregation is relatively small, as the average size of the Pt particles remains approximately 2nm. In contrast, when a high temperature oxidation/reduction treatment is used to activate the Pt40-dendrimer/γ-Al2O3 material, sintering of Pt is observed and the average Pt particle size increases to approximately 4nm. Kinetic data obtained with Pt/γ-Al2O3 catalysts activated under both protocols for the structure-insensitive CO oxidation and the structure-sensitive ethane hydrogenolysis reactions underline the differences in the sizes of the Pt particles in these materials, consistent with previous literature reports.

Investigation of Pt/γ-Al2O3Catalysts Prepared by Sol–Gel Method: XAFS and Ethane Hydrogenolysis

The physical and chemical properties of alumina-supported Pt prepared by sol–gel method were investigated using BET surface area measurement, hydrogen chemisorption, transmission electron microscopy, X-ray powder diffraction, and X-ray absorption fine structure (XAFS). The BET surface area, pore size, and pore volume of Pt/γ-Al2O3obtained from sol–gel method were similar to those of impregnated catalysts. The result of XAFS showed that the platinum particles consisted of 20 atoms, ca 1 nm, independent of the preparation method. However, the available metal surface area in the sol–gel catalysts for hydrogen chemisorption decreased by as much as 30%, compared to the impregnated catalyst. The turnover frequency of ethane hydrogenolysis reaction was considerably lower than that of the impregnated catalyst. Thus, we concluded that the platinum particles in the Pt/γ-Al2O3sol–gel catalysts were buried in the γ-Al2O3. This burial of particles was the cause of a strong metal support interaction and resulted in high sintering resistance of metal particles at 873 K in air.

Ultrafine nickel particles generated by laser-induced gas phase photonucleation

A UV laser-assisted gas phase photonucleation process is used to generate nickel ultrafine particles(UFPs) from ambient temperature Ni(CO) 4 precursor. The nanostructure and morphology of the UFPs are characterized by transmission electron microscopy (TEM) and X-ray diffractometry (XRD). Using ethane hydrogenolysis to probe the reactivity of the nickel UFPs as heterogeneous catalysts, we find that these UFPs show high reactivity and extraordinary resistance to deactivation. XRD analysis reveals a hexagonal Ni 3C phase in those UFPs that were used to catalyze the ethane hydrogenolysis reaction in excess ethane.

Formation of small Pt-Ir bimetallic clusters in NaY zeolite probed with 129Xe NMR spectroscopy and ethane hydrogenolysis

Very small (about 1 nm) and homogeneous Pt-Ir bimetallic clusters were formed in the zeolite supercage by calcining NaY co-ion-exchanged with Pt(NH 3) 2+ 4 and Ir(NH 3) 5C1 2+ at room temperature and subsequent reduction treatment with H 2 at 573 K. These bimetallic clusters were characterized by hydrogen and xenon adsorption, X-ray differaction (XRD), 129Xe NMR spectroscopy, and ethane hydrogenolysis reaction. Pt-Ir bimetallic clusters showed specific characteristics different from those of Pt and Ir monometallic clusters and physical mixtures of corresponding monometallic clusters. The chemical shifts of Pt-Ir bimetallic clusters in 129Xe NMR and their catalytic activities in ethane hydrogenolysis were lower than those of the corresponding physical mixtures of Pt and Ir monometallic clusters. The activation energies of Pt-Ir bimetallic clusters in ethane hydrogenolysis were smaller than those of monometallic Pt and Ir clusters. The turnover frequencies (TOFs) of bimetallic clusters in ethane hydrogenolysis are widely different from those of monometallic clusters.

Potassium dispersion on silica-supported ruthenium catalysts

Alkali modifiers are known to be quite effective at improving catalyst activity or selectivity for several metal-catalyzed reactions of industrial importance. Yet it is still difficult to address the location and distribution of alkali species in most catalysts. This paper reports on an investigation of the potassium dispersion in a series of 3 wt% Ru/SiO 2 catalysts sequentially doped with potassium nitrate up to (K/Ru)awm = 0.2 followed by rereduction. This series was evaluated extensively using gas volumetric hydrogen chemisorption and the structure-sensitive ethane hydrogenolysis reaction. Hydrogen chemisorption results indicate that the alkali was apparently atomically dispersed on the ruthenium surface. The added potassium species interfered with hydrogen chemisorption on a one-to-one atomic basis. Potassium addition resulted in a decrease in the apparent activation energy and an increase in the apparent hydrogen reaction order for ethane hydrogenolysis. Using the statistical poisoning model of Martin ( Catal. Reu.-Sci. Eng. 30, 519 (1988)) which assumes that the metal surface is uniform for adatom adsorption, the apparent ensemble required for the reaction was estimated to be made up of 12 ± 3 adjacent exposed surface ruthenium atoms. Using an extension of Martin's model, this structure-sensitive reaction also revealed that at the higher potassium levels the alkali dispersion became nonuniform. This nonuniform dispersion is suggested to be due to a preference of the dopant for certain metal sites. Because of this nonuniform dispersion, the “true” reaction ensemble size is suggested to be less than 12.

Rhodium-niobia interaction in niobia-promoted Rh/SiO 2 catalysts: formation of RhNbO 4 on SiO 2

Rhodium-niobia interaction in both Nb 2O 5-promoted Rh/SiO 2 catalysts and rhodium double oxide (RhNbO 4) catalysts has been studied by XRD, XPS, EXAFS and FT-IR, and catalytic properties were examined in relation to the catalyst structures. The extent of Rh-Nb 2O 5 interaction in Nb 2O 5-promoted Rh catalysts was sensitive to preparation variables such as the Nb/Rh ratio, the SiO 2 used, and the calcination temperature (the formation of RhNbO 4). Fine particles of RhNbO 4 supported on SiO 2 showed considerably high catalytic activity in ethane hydrogenolysis reaction, and this result was discussed in terms of an important role of a highly-oxidized state of rhodium ion.

Kinetics of ethane hydrogenolysis over silica-supported ruthenium-group IB metal catalysts

We have studied the ethane hydrogenolysis reaction to determine the effect of adding copper and silver to a silica-supported ruthenium catalyst. Specific activities were measured at a number of temperatures as a function of the fraction of Group IB metal. In addition, the effect of changing the ratio of hydrogen to ethane in the feed gas was used to measure apparent orders of reaction as a function of temperature and Group IB metal added. At the lower temperatures studied we found that the effect of adding copper or silver to the catalyst was virtually the same, the differences being attributed to the greater affinity of copper for defect-like sites on the ruthenium crystallites. At higher temperatures, copper and silver acted differently; copper seemed to be active for the removal of site-blocking hydrogen from the active ruthenium surface, while silver merely blocked the ruthenium sites most active for the removal of hydrogen from the surface. We postulate that the defect-like sites of supported ruthenium crystallites are most active for the desorption of weakly adsorbed hydrogen while the actual carbon-carbon bond cleavage takes place on the basal planes. The increase in specific activity observed as the dispersion of the catalyst decreased was attributed to the increase in relative number of carbon-carbon bond-breaking sites. The order of reaction with respect to hydrogen partial pressure suggests that the adsorbed hydrocarbon intermediate has a stoichiometry of C 2H 3.

Ethane hydrogenolysis over well-defined [formula omitted] catalysts

This work was undertaken to investigate the behavior of the ethane hydrogenolysis reaction over well-characterized, chlorine-free, silica-supported ruthenium-copper catalysts. The total dispersion of all catalysts was about 29%. The reaction studies were carried out in a laboratory-scale reactor, and catalyst activity was correlated with ruthenium surface composition, as measured previously by using nuclear magnetic resonance spectroscopy of chemisorbed hydrogen. Monte Carlo simulations of the catalyst were used to assist in the interpretation of the results. The reaction studies indicate that catalysts with a Cu: Ru atom ratio greater than 1:9 have a constant specific activity (rate per surface ruthenium atom), analogous to the behavior of single crystal surfaces. Below this Cu: Ru ratio, the specific activity drops rapidly as copper is added to the system at the lower temperatures studied. At a Cu: Ru ratio of 1:9 the modeling suggests that all edge and corner sites of the catalyst crystallite are occupied by copper. We conclude that the ethane hydrogenolysis reaction over silica-supported ruthenium-copper catalysts is sensitive to the crystallite structure but no geometric effects are observed.

Cyclohexane dehydrogenation over a strained-layer [formula omitted] catalyst

The present studies are part of a continuing effort to identify those properties of a bimetallic system which can be related to its special catalytic properties. The specific model system of Cu and Ru was chosen due to the immiscibility of these two metals as well as the pivotal role played by this metal pair in historical bimetallic studies. The immiscibility of these two metals facilitates coverage determination by temperature-programmed desorption (TPD) and circumvents the many complications associated with the assay of alloy surface composition. The results are discussed from previous studies which have addressed the geometric and electronic structure of Cu overlayers on Ru(0001), the adsorption of CO and H/sub 2/ on submonolayer-to-multilayer deposits of Cu, as well as the measurement of the high-pressure kinetics of the methanation and ethane hydrogenolysis reactions on this model bimetallic catalyst. These results suggest that Ru specific rates for methanation and ethane hydrogenolysis on supported Cu/Ru catalysts approximate those values found for pure Ru. As a consequence, the rates for the cyclohexane dehydrogenation reaction on supported Cu/Ru, similarly corrected, must exceed those specific rates found for pure Ru. (The uncorrected specific rates for the supported Cu/Ru system remain essentially unchanged upon addition ofmore » Cu to Ru.) An activity enhancement for cyclohexane dehydrogenation in the mixed Cu/Ru system relative to pure Ru is most surprising given that Cu is less active for this reaction than Ru. In this note, the authors report just such an activity enhancement for the addition of Cu to a model Ru(0001) catalyst. 16 references.« less

Fischer-Tropsch synthesis on bimetallic ruthenium-gold catalysts

The effect of Au in the behavior of Ru as a Fischer-Tropsch catalyst was studied. Two series of catalysts were investigated, one supported on SiO 2 and the other on MgO. Au did not seem to alter the product distribution on Ru at pressures up to 1 MPa and in the temperature range 490–570 K. However, the turnover frequencies for both CO hydrogenation and methanation showed a precipitous drop with the Au content in the SiO 2-supported catalysts, whereas on the MgO series a maximum in activity was observed at an intermediate Au content. These activity patterns were correlated with extensive physical characterization placing major emphasis on analytical electron microscopy. The activity trends as a function of Au content were remarkably similar to those previously reported for the structure-sensitive ethane hydrogenolysis reaction. In both reactions, the effect of Au appears to be due to a dilution of the active Ru ensembles.