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.
Highlights
Carbonaceous materials have been widely used as supports of metal-based catalysts under various forms: activated carbon, carbon black, multiwall carbon nanotubes, nanostructured carbon replicas (OMC) synthesized by templating methods [1, 2]
Two series of mesoporous carbons were synthesized through a hard-templating method using the SBA-15 or disordered mesoporous silica gel as the templates and furfuryl alcohol or sucrose as the carbon sources
All the synthesized carbon replicas characterized by low crystallinity and both sucrosederived carbons displayed higher surface area and mesopore volume than furfuryl alcohol-derived counterparts
Summary
Carbonaceous materials have been widely used as supports of metal-based catalysts under various forms: activated carbon, carbon black, multiwall carbon nanotubes, nanostructured carbon replicas (OMC) synthesized by templating methods [1, 2]. Its counterpart synthesized using furfuryl alcohol precursor was characterized by a somewhat lower surface area [24] This synthesis procedure is adopted in the present work in order to prepare the mesoporous carbons of potential application as supports for the Pd catalysts. The flat adsorption configuration has been associated with a strong interaction between the metal and the π bonds in the furan ring, originating from an sp to sp rehybridization On these metals, the reactions involve both the furan ring and the aldehyde group and the products of hydrogenation, hydrogenolysis, decarbonylation can be formed. The aim of our experiments was to elucidate the effect exerted by the particular carbon support on the formation of Pd active sites for the furfural hydrogenation studied in 2-propanol solvent under mild reaction conditions (35 °C, 6 bar H2)
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