NMR-STUDY OF THE INFLUENCE OF ADSORBED SULFUR ON HYDROGEN CHEMISORPTION ON SUPPORTED RUTHENIUM CATALYSTS

NMR of hydrogen chemisorbed on silica-supported ruthenium catalysts was used to study the dissociation of H2S and its effect on subsequent hydrogen adsorption. A mixture of H2S/He was used to sulfide the reduced catalyst. The hydrogen coverages resulting from the dissociation of H2S as measured by NMR yielded estimates of sulfur coverages in good agreement with the results of X-ray fluorescence analysis of sulfur on the samples. The H2S dissociation reaction was found to be enhanced on higher dispersion catalysts suggesting an important role for defect-like sites. At sulfur coverages greater than 0.25 sulfur atoms per surface ruthenium atom, no hydrogen from the dissociation of H2S could be detected remaining on the surface. On the presulfided catalysts dosed to saturation with additional hydrogen, the NMR spectra revealed the presence of two species of hydrogen: a mobile species and a less mobile species. At sulfur coverages greater than 0.5 no detectable hydrogen could be adsorbed on the surface when exposed to 30 Torr of H2. The ratio of weakly bound hydrogen to the strongly bound hydrogen at saturation coverage decreased with increasing sulfur coverage. The small change in the magnitude of the NMR lineshift of hydrogen-on-metal with sulfur coverage suggested that the adsorbed sulfur does not induce a strong electronic effect on the chemisorption of hydrogen. © 1992.