Pulse-response TAP studies of the reverse water–gas shift reaction over a Pt/CeO 2 catalyst

Abstract

The temporal analysis of products (TAP) technique was successfully applied for the first time to investigate the reverse water–gas shift (RWGS) reaction over a 2% Pt/CeO 2 catalyst. The adsorption/desorption rate constants for CO 2 and H 2 were determined in separate TAP pulse-response experiments, and the number of H-containing exchangeable species was determined using D 2 multipulse TAP experiments. This number is similar to the amount of active sites observed in previous SSITKA experiments. The CO production in the RWGS reaction was studied in a TAP experiment using separate (sequential) and simultaneous pulsing of CO 2 and H 2. A small yield of CO was observed when CO 2 was pulsed alone over the reduced catalyst, whereas a much higher CO yield was observed when CO 2 and H 2 were pulsed consecutively. The maximum CO yield was observed when the CO 2 pulse was followed by a H 2 pulse with only a short (1 s) delay. Based on these findings, we conclude that an associative reaction mechanism dominates the RWGS reaction under these experimental conditions. The rate constants for several elementary steps can be determined from the TAP data. In addition, using a difference in the time scale of the separate reaction steps identified in the TAP experiments, it is possible to distinguish a number of possible reaction pathways.