The rate of methane formation by decomposition of methanol is studied at temperatures between 473 and 583 K and methanol pressures between 0.2 and 10.4 kPa. Coverages of adsorbed species are measured using temperature-programmed hydrogenation (TPH), temperature-programmed desorption (TPD), and magnetic measurements. The reaction system can be adequately described assuming the decomposition of methanol to proceed in two steps, viz. a decomposition into CO and H2 followed by methanation of CO. The former reaction is much more rapid than the latter. Assuming CH hydrogenation to be rate-determining, the rate of methane formation could be described by the LHHW rate equation TOF = 1.2 × 105e- -68 RTp1.5 (1 + 1.8 × 10-1e 15 RTp0.5 + 3.1 × 10-16 e 144 RTp)2 TOF is the turnover frequency in s-1, p is the methanol pressure in kPa, T is the temperature in K, and R = 8.314 × 10-3kJ mol-1 K-1. Coverages of adsorbed species predicted by this equation differ strongly from results obtained by measurements of total surface coverages using TPH, TPD, and magnetic measurements. This has been interpreted as an indication that the number of surface sites actively participating in the methanation reaction composes only a small fraction of the total number of sites.@en

The kinetics of the formation of methane from methanol have been studied on a 50 wt% Ni/SiO₂, a 20 wt% Ni/SiO₂, a 10 wt% Ni/Al₂O₃ and a 5 wt% Ni/TiO₂ 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/H₂ = 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/SiO₂, 50 wt% Ni/SiO₂, 10 wt% Ni/Al₂O₃, 5 wt% Ni/TiO₂. 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/TiO₂ when CO/H₂ was used as the reactant gas instead of CH₃OH. The observations were explained assuming a mechanism in which methapnol first decomposes into CO and H₂ 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/H₂. Due to the presence of chemically altered sites on TiO₂-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/H₂. The higher selectivity towards higher hydrocarbons as well as the higher deactivation rates are also explained assuming the presence of chemically altered sites.

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