A detailed spectroscopic analysis of the growth of oxy-carbon species on the surface of Pt/Al2O3 during propane oxidation

• Casey P. O'Brien, 
• Ivan C. Lee^, 

• U.S. Army Research Laboratory, Sensors and Electron Devices Directorate, 2800 Powder Mill Road, Adelphi, MD 20783, USA

Received 3 March 2016, Revised 2 November 2016, Accepted 28 December 2016, Available online 21 January 2017

http://dx.doi.org/10.1016/j.jcat.2016.12.021

Keywords

• Propane oxidation; 
• Platinum; 
• Carbon; 
• Spectroscopy

Highlights

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Many different oxy-carbon species are formed on Pt and spill over onto Al₂O₃.

•

Enolate, ester, and acetone species are more reactive than acetate species.

•

The concentration of oxy-carbon species does not correlate with the CO₂ production rate.

•

Oxy-carbon surface species are inert spectators in the propane oxidation mechanism.

Abstract

The growth of oxygenated carbonaceous (oxy-carbon) species on the surface of Pt/Al₂O₃ during total oxidation of propane is analyzed in detail—including their composition, their location on the catalyst surface, their reactivity, and their role in the propane oxidation mechanism—by in situ diffuse reflectance infrared Fourier-transform spectroscopy (DRIFTS). Platinum nanoparticles catalyze the transformation of propane into many different oxy-carbon surface species, including acetate, enolate, aliphatic ester, and acetone, which spillover and grow on the Al₂O₃ support. There is no correlation between the concentration of oxy-carbon surface species and the rate of CO₂production in the gas-phase, which indicates that these species are inert spectators in the propane oxidation mechanism. Temperature-programmed oxidation of the oxy-carbon surface species reveals that enolate, aliphatic ester, and acetone species are removed from the surface by combustion at similar temperatures with an activation barrier of 112 kJ/mol, whereas acetate species are removed at higher temperatures with an activation barrier of 147 kJ/mol. Both the formation and combustion of oxy-carbon surface species occur in pathways that are parallel to, and orders-of-magnitude slower than, the main pathway to CO₂ production.