Insights into support effects of Ag/SiO2 catalysts for dimethyl glycolate semi-hydrogenation to methyl glycolate
Support materials play vital roles in heterogenous catalysis via the so-called support effects, and understanding on the support effects is beneficial for the design of high-performance catalysts. Herein, we represent detailed investigations on the support effects of Ag catalysts for dimethyl glycolate (DMO) semi-hydrogenation to methyl glycolate (MG), where G6 silica with amorphous mesopores, SBA-15 with parallel mesopores and silica nanospheres (MSNS) with center-radial ones were employed as the supports. The hydrogenation activity decreases in the order of Ag/MSNS > Ag/SBA-15 > Ag/G6 while the MG selectivity in the order of Ag/G6 > Ag/MSNS > Ag/SBA-15 at the same reaction conditions, indicating remarkable support effects on both activity and selectivity. Structural characterizations, temperature programmed experiments and in-situ FTIR of DMO adsorption experiments demonstrate that the weak confinement effect of G6 leads to the larger sized Ag nanoparticles and weakened activation of DMO and H 2 , which contributes to low hydrogenation activity. In contrast, the ordered mesoporous SBA-15 and MSNS deliver well confinement effects for Ag nanoparticles and the activation of DMO and H 2 , but the distinct pore structures result in different activation and diffusion behaviors. Finally, DMO conversion and MG yield are well correlated with the competitive adsorption of H 2 versus DMO on Ag catalysts, indicating such competitivity as a descriptor for DMO semi-hydrogenation over Ag catalysts.
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