(544cf) Platinum Vs. Ruthenium: A Kinetic Comparison of Vapor-Phase Acetone Hydrogenation

Xin Gao¹, Omar A. Abdelrahman², Jesse Q. Bond^1,*

1. Department of Biomedical and Chemical Engineering, Syracuse University, Syracuse, NY 13244, United States.
2. Department of Chemical Engineering, University of Massachusetts Amherst, Amherst, MA 01003, United States.

As one of the most significant and fundamental strategies of biomass conversion, hydroprocessing of carbonyl compounds plays a central role in converting bio-based feedstocks to chemicals and fuels. For example, furfural hydrogenation to produce furfuryl alcohol involves the reduction of an aldehyde group, while the hydrogenation of levulinic acid (LA) to form g-valerolactone (GVL) is, essentially, ketone hydrogenation. In order to design more active, stable, and selective catalysts for carbonyl hydrogenation, it is important to understand the governing kinetics at an elementary level on a variety of catalytic materials. Platinum group metals (PGMs), such as platinum (Pt) and ruthenium (Ru) are both widely used in carbonyl hydrogenation, yet there are subtle differences between the two. For example, Ru has been largely reported as an efficient catalyst for carbonyl hydrogenation in aqueous media, whereas platinum (Pt) is reportedly more active for analogous hydrogenations in the vapor phase. Presently, there is no consensus within the field regarding the elementary-level origins of these differences; accordingly, we have undertaken a comprehensive microkinetic analysis of carbonyl hydrogenation on both metals, and attempt to provide mechanistic explanations for our macroscopic observations.

Due to the similar and comparable kinetic and thermodynamic trends of aliphatic ketone with different lengths of carbon chains, acetone is the most basic ketone that needs to be comprehensively investigated for achieving the goal of understanding other carbonyl compounds. Vapor phase acetone hydrogenation experiments were carried out at different temperatures and partial pressures for both supported Pt and Ru catalysts. Ru was found to be more intrinsically active than Pt during vapor phase hydrogenation; however, Pt is far more stable, which gives the appearance of a more active material under steady state conditions. For both metals, apparent reaction orders, barriers, and kinetic isotope effects during H2/D2 switching experiments were measured to help distinguish between proposed reaction mechanisms and likely rate determining steps. Finally, we conducted a microkinetic analysis of the system, complete with regression of sensitive parameters for the two metals, which provides an explanation for macroscopically observable differences between the two metals.