In Situ Strong Metal–Support Interaction (SMSI) Affects Catalytic Alcohol Conversion

Strong metal–support interactions (SMSIs) and catalyst deactivation have been heavily researched for decades by the catalysis community. The promotion of SMSIs in supported metal oxides is commonly associated with H2 treatment at high temperature (>500 °C), and catalyst deactivation is commonly attributed to sintering, leaching of the active metal, and overoxidation of the metal, as well as strong adsorption of reaction intermediates. Alcohols can reduce metal oxides, and thus we hypothesized that catalytic conversion of alcohols can promote SMSIs in situ. In this work we show, via IR spectroscopy of CO adsorption and electron energy loss spectroscopy (EELS), that during 2-propanol conversion over Pd/TiO2 coverage of Pd sites occurs due to SMSIs at low reaction temperatures (as low as ∼190 °C). The emergence of SMSIs during the reaction (in situ) explains the apparent catalyst deactivation when the reaction temperature is varied. A steady-state isotopic transient kinetic analysis (SSITKA) shows that the intrinsic reactivity of the catalytic sites does not change with temperature when SMSI is promoted in situ; rather, the number of available active sites changes (when a TiOx layer migrates over Pd NPs). SMSI generated during the reaction fully reverses upon exposure to O2 at room temperature for ∼15 h, which may have made their identification elusive up to now.