Zeolite and metal oxide catalysts for the production of dimethyl sulfide and methanethiol

Metal oxide and zeolite catalysts were examined to determine their suitability for the production of methanethiol and dimethyl sulfide from the condensation of methanol and hydrogen sulfide. Fixed bed reactor experiments were used to test the catalysts in these processes. The acid sites of these catalysts were characterized by investigating the thermal desorption of 1-propanamine from these sites. It was found that WO3/ZrO2, La2O3/Al2O3, g-Al2O3, and HZSM-5 catalysts were active and selective in the production of dimethyl sulfide. On these four catalysts, the reaction converting methanol to dimethyl ether and the methanethiol disproportionation reaction were fast and close to equilibrium. The yield to dimethyl ether was high at short contact times and decreased with increased contact time. The WO3/Al2O3 catalyst was less active than these four, but was selective to methanethiol. For these catalysts, the selectivity to sulfur products did not decrease as the methanol partial pressure varied over orders of magnitude, indicating that the sulfidation reactions are close to zero order in methanol. The MoO3/SiO2, TiO2/SiO2, SAPO-18, and AlPO-18 catalysts were not suitable for production of either product due to low activity or selectivity. Acid site characterization experiments showed that sites desorbing 1-propanamine and its reaction products at temperatures between 300 and 350ºC were the most active in the sulfidation of methanol. Based on this work and results in the literature, a mechanism was proposed that correlates methanethiol selectivity to catalyst acid strength. In additional work, X-ray absorption spectroscopy was used to characterize metal doped CeO2/Al2O3 catalysts active for the condensation of carboxylic acids to ketones. No general correlation was found between the number of oxygen vacancies measured by Ce LIII XANES and the activity of a catalyst for this reaction. It was found by Co K edge XANES and EXAFS that cobalt atoms doped into this catalyst are substituted for cerium atoms in the CeO2 lattice and are coordinated tetrahedrally by four oxygen atoms. Pd LIII edge XANES showed that palladium doped into the CeO2/Al2O3 catalyst mostly dissolves in the CeO2 lattice in a highly ionic state