Rhenium
substantially promotes the rate of Pt-catalyzed glycerol
hydrogenolysis to propanediols and shifts the product selectivity
from 1,2-propanediol to a mixture of 1,2 and 1,3-propanediols. This
work presents experimental evidence for a tandem dehydration–hydrogenation
mechanism that occurs over a bifunctional Pt–Re catalyst. Infrared
spectroscopy of adsorbed pyridine and the rate of aqueous-phase hydrolysis
of propyl acetate were used to identify and quantify Brønsted
acid sites associated with the Re component. Near-ambient-pressure
XPS revealed a range of Re oxidation states on the Pt–Re catalysts
after reduction in H<sub>2</sub> at 393 and 493 K, which accounts
for the presence of Brønsted acidity. A mechanism involving acid-catalyzed
dehydration followed by Pt-catalyzed hydrogenation was consistent
with the negative influence of added base, a primary kinetic isotope
effect with deuterated glycerol, an inverse isotope effect with dideuterium
gas, and the observed orders of reaction
