High Structure Sensitivity of Vapor-Phase Furfural Decarbonylation/Hydrogenation Reaction Network as a Function of Size and Shape of Pt Nanoparticles

Vapor-phase transformations of furfural in H-2 over a series of Pt nanoparticles (NPs) with various particle sizes (1.5-7.1 nm size range) and shapes (rounded, cubes, octahedra) encapsulated in poly(vinylpyrrolidone) (PVP) and dispersed on MCF-17 mesoporous silica were investigated at ambient pressure in the 443-513 K temperature range. Furan and furfuryl alcohol (FFA) were two primary products as a result of furfural decarbonylation and hydrogenation reactions, respectively. Under conditions of the study both reactions exhibited structure sensitivity evidenced by changes in product selectivities, turnover rates (TORs), and apparent activation energies (E-A's) with Pt particle size and shape. For instance, upon an increase in Pt particle size from 1.5 to 7.1 nm, the selectivity toward FFA increases from 1% to 66%, the TOR of FFA production increases from 1 x 10(-3) s(-1) to 7.6 X 10(-2) s(-1), and E-A decreases from 104 kJ mol(-1) to 15 kJ mol(-1) (9.3 kPa furfural, 93 kPa H-2, 473 K). Conversely, under the same experimental conditions the decarbonylation reaction path is enhanced over smaller nanoparticles. The smallest NPs (1.5 nm) produced the highest selectivity (96%) and highest TOR values (8.8 x 10(-2) s(-1)) toward furan formation. The E-A values for decarbonylation (similar to 62 kJ mol(-1)) was Pt particle size independent. Furan was further converted to propylene via a decarbonylation reaction, but also to dihydrofuran, tetrahydrofuran, and n-butanol in secondary reactions. Furfuryl alcohol was converted to mostly to 2-methylfuran.