Effect of the type of siliceous template and carbon precursor on physicochemical and catalytic properties of mesoporous nanostructured carbon-palladium systems

Abstract

Two series of nanostructured carbon replicas were synthesized through a hard-templating method using ordered SBA-15 or disordered mesoporous spherical silica gel as the templates and furfuryl alcohol or sucrose as the carbon source. They were explored to synthesize the Pd catalysts (ca. 1.5 wt% Pd loading) by the colloid-based microemulsion procedure which allowed preparing the catalysts of monodispersed Pd particles of similar size (4–5 nm). The palladium phase in the catalysts (e.g. the Pd particles distribution and extent of agglomeration) varied depending on the textural and surface characteristics of the carbon replicas. In the furfural hydrogenation studied as a probe reaction (2-propanol, 35 °C, 6 bar H2), furfuryl alcohol and tetrahydrofurfuryl alcohol were the major products formed. The catalytic reactivity has been related to the properties of the Pd phase including the surface Pd concentration and the extent of the Pd particles aggregation accompanied by the nearest palladium environment expressed by the surface O/Pd atomic ratio. At high O/Pd ratio the reaction slowed down because of a facilitated furfuryl alcohol adsorption resulting most probably in a blockage of the active sites. The SiO2 sucrose system provided the catalyst which was characterized by relatively low O/Pd ratio with well-dispersed Pd particles and the highest and stable activity for the furfural hydrogenation. The SBA-series catalysts, with lower O/Pd and more aggregated Pd particles, exhibited lower activity but somewhat higher tendency to the tetrahydrofurfuryl alcohol formation.