Rate Of CO Hydrogenation Research Articles

The influence of propylene on CO hydrogenation over silica-supported ruthenium

Reactions of C 3H 6, H 2, and CO were studied over Ru SiO 2 . Processes of hydrocarbon chain growth were investigated by comparing product distributions observed in the reactions of C 3H 6 and H 2, and of C 3H 6, H 2, and CO. In the latter experiments, the source of carbon in the products was identified by using 13C-labeled CO and unlabeled C 3H 6 and analyzing the products by isotope-ratio gas chromatography-mass spectrometry. Hydrogenation to C 3H 8 is the dominant reaction in the absence of CO. Small conversions of C 3H 6 to CH 4, C 2H 6, and C 4+ products are also observed. Schemes for C 3H 6 hydrogenolysis and hydrogenation are discussed and a chain growth mechanism for C 3H 6 homologation is proposed. The latter involves C 1, C 2, and C 3 monomer units and is shown to describe the observed product distribution. The presence of CO enhances homologation relative to hydrogenolysis and suppresses hydrogenation. The addition of C 3H 6 to a CO H 2 feedstream reduces the rate of CO hydrogenation to form hydrocarbons. However, the overall rates of production of C 4+ hydrocarbons increase with increasing C 3H 6 partial pressure as a result of C 3H 6 homologation. The formation of butanal and butanol via hydroformylation is also observed. Comparisons between the reactions of C 2H 4 and C 3H 6 are made and implications of their similarities and differences are discussed.

Methane formation from methanol on Ni/SiO 2, Ni/Al 2O 3 and Ni/TiO 2 catalysts

The kinetics of the formation of methane from methanol have been studied on a 50 wt% Ni/SiO 2, a 20 wt% Ni/SiO 2, a 10 wt% Ni/Al 2O 3 and a 5 wt% Ni/TiO 2 catalyst. Temperatures were typically between 475 and 585 K with methanol partial pressures between 0.2 and 10.4 kPa. The results were compared with data obtained using a CO/H 2 = 0.5-mixtures as the reactant gas. The apparent activation energy for methane formation was independent of the support. Specific rates (TOF's) increased in the order 20 wt%Ni/SiO 2, 50 wt% Ni/SiO 2, 10 wt% Ni/Al 2O 3, 5 wt% Ni/TiO 2. Both deactivation rates and selectivity towards higher hydrocarbons increased in the same order. Contrary to the results obtained on the other catalysts, methane formation rates are much larger on Ni/TiO 2 when CO/H 2 was used as the reactant gas instead of CH 3OH. The observations were explained assuming a mechanism in which methapnol first decomposes into CO and H 2 followed by the hydrogenation of CO. In case of silica and alumina supported catalysts the first reaction is much faster than the latter and the rate of methane formation from methanol equals the rate of methane formation from CO/H 2. Due to the presence of chemically altered sites on TiO 2-supported nickel the rate of the first reaction (a dehydrogenation) is decreased, whereas the rate of CO-hydrogenation is known to increase strongly. This causes the rate of methane formation from methanol to be lower than the rate of methane formation from CO/H 2. The higher selectivity towards higher hydrocarbons as well as the higher deactivation rates are also explained assuming the presence of chemically altered sites.

The effects of titania and alumina overlayers on the hydrogenation of CO over rhodium

Submonolayer quantities of TiOx and AlOx were deposited on a polycrystalline Rh foil. The samples were characterized by Auger electron spectroscopy and then enclosed in an atmospheric-pressure chamber to evaluate their activity for CO hydrogenation. AlOx deposition suppresses the rate of CO hydrogenation in direct proportion to the AlOx coverage, but the product distribution and kinetics are unaffected. These observations indicate that the only effect of AlOx is to block Rh sites. TiOxdeposition has a more complex effect. With increasing TiOx coverage, the methanation rate passes through a maximum at a TiOx coverage of 0.15 monolayer. The maximum rate is three times as large as the rate of clean Rh. The deposited TiOx also affects the catalyst selectivity as well as the kinetics of methane formation. The selectivity for methane reaches a minimum for a TiOx coverage of ca. 0.20 monolayer and in the same range the activation energy for methanation reaches a minimum and the H2 and CO partial pressure dependences reach a maximum. The unusual behaviour of TiOx-promoted Rh is attributed to the occurrence of highly active catalytic sites near the perimeter of the TiOx islands making up the overlayer.

Hydrogenation of carbon dioxide and carbon monoxide over supported platinum catalysts

The production of methanol from reactions between CO2+ H2 and CO + H2 has been studied over platinum catalysts supported on Nb2O5, ZrO2, MgO, SiO2 and TiO2. Zirconia- and niobia-supported Pt catalysts showed the highest activity for reactions of both CO2 and CO. The magnesia-supported Pt catalyst was less active compared with Pt/ZrO2 and Pt/Nb2O5, but exhibited the highest selectivity towards MeOH formation. The activation energy of the CO2+ H2 reaction was always lower than that of the CO reaction. Thus, the reaction of CO2+ H2 occurs easily at lower temperature compared with the CO + H2 reaction, but the rate of CO hydrogenation exceeds that of CO2 hydrogenation at higher temperatures. The selectivity towards methanol was higher for CO2 hydrogenation than that for the CO + H2 reaction over all the catalysts used.

Application of transient response techniques for quantitative determination of adsorbed carbon monoxide and carbon present on the surface of a ruthenium catalyst during Fischer-Tropsch synthesis

Transient response experiments using isotopic tracers have been carried out to determine quantitatively the coverages of adsorbed CO and carbon on a Ru SiO 2 catalyst during Fischer-Tropsch synthesis. In situ infrared spectra reveal that the Ru surface is virtually saturated by chemisorbed CO. The rate of exchange of adsorbed and gas-phase CO is very rapid compared to the steady-state rate of CO hydrogenation. The integrated absorption coefficient for adsorbed CO is found to decrease from 9.0 × 10 7 to 4.5 × 10 7 cm/mol as θ CO increases from 0 to 1.0. Two forms of carbon, C α and C β, are also present on the catalyst surface under normal reaction conditions, neither of which is associated with oxygen or hydrogen. C α is much more reactive than C β. The surface coverage of C α rapidly comes to a steady-state value and the steady-state rate of methane formation is found to be a linear function of the C α coverage. The coverage of C β is considerably larger than that of C α and continues to grow over a period of up to 5 min under reaction conditions. C β is formed from C α in the presence of adsorbed hydrogen and can be converted back to C α. It is concluded that at least a part of the C β deposited resides on the support and that the rest is present on the surface of Ru, and may be responsible for the gradual loss of methanation activity with time. The dependencies of the coverages of C α and C β on the partial pressures of the reactants have been determined and are found to be quite different from one another.

Heterogeneous methanation: Steady-state rate of CO hydrogenation on supported ruthenium, nickel and rhenium

A study has been made of initial activity, steady-state activity and activity in the presence of H 2S for CO hydrogenation on a number of supported catalysts. Initial rates of CO hydrogenation were found to be similar on Ni Al 2O 3 , Ni ZrO 2 and Raney Ni catalysts when corrected for metal surface area. Under steady-state conditions, the specific reaction rate was a factor of 25 lower and the activities were in the order Raney Ni > Ni Al 2O 3 > Ni ZrO 2 . In the presence of 10 ppm of H 2S the activity decreased by an additional factor of 10 and the order was Ni ZrO 2 Ni Al 2O 3 ⪢ Raney Ni . The support has an appreciable effect on the extent of deactivation at steady state and the activity in the presence of sulfur-containing compounds. In addition, a comparison was made of the specific activity of supported Ni, Ru and Re catalysts at steady state and in sulfur-containing streams.

Heterogeneous methanation: Initial rate of CO hydrogenation on supported ruthenium and nickel

The initial rate of reaction of hydrogen and carbon monoxide was measured on supported Ru and Ni catalysts in a differential batch reactor. Using hydrogen adsorption to determine Ru and Ni surface areas, initial rates for methane and total hydrocarbon formation were expressed as turnover numbers. The initial rate of supported ruthenium was found to be independent of ruthenium particle size from < 10 to 90 Å. Nickel exhibited turnover numbers twice as high as Ru at 280 °C and activation energies of 20 and 28 kcal mole −1 for total hydrocarbon and methane formation compared to 17 and 24 kcal mole −1 for Ru.