Correlation between deactivation and Pt-carbonyl formation during toluene hydrogenation using a H2/CO2 mixture

H2/CO2 mixtures derived from biomass degradation may be regarded as a renewable source of hydrogen that could be used for hydrogenation reactions. The practicality of directly using a CO2-containing H2 feed was evaluated during the hydrogenation of toluene to methylcyclohexane at 75 °C and ambient pressure. An operando DRIFTS study was carried out to unravel some of the mechanistic features of this reaction over a 0.88% Pt/Al2O3 catalyst, in particular to rationalize the loss of activity observed in the presence of CO2. We report, for the first time, a quantitative link between the loss of activity for hydrogenation and the formation of carbonyls adsorbed on the platinum, while the deactivation could not be correlated to the species formed onto the alumina, e.g. carbonates, hydrogenocarbonates and formates.

The loss of toluene hydrogenation activity is due to the formation of Pt-carbonyl species when using a CO2-containing feed.Figure optionsDownload high-quality image (32 K)Download as PowerPoint slideResearch highlights
► Toluene adsorbed both on the metal and the alumina under our experimental conditions.
► The utilization of a mixture of H2 and CO2 for the hydrogenation of toluene at 75 °C resulted in the formation of Pt-carbonyl species that strongly poisoned the catalyst.
► An unequivocal relation was obtained between the level of toluene conversion and the Pt-carbonyl band intensity.
► The formation of many surface species on the alumina (e.g. carbonate, hydrogenocarbonate, formate) was not related to the sample deactivation under our experimental conditions.