Ethane Dehydrogenation with CO2 as a soft oxidant over a Cr-TUD-1 catalyst

A Cr-TUD-1 catalyst was directly synthesized under hydrothermal conditions using triethanolamine as a template for mesopore formation, tetraethylorthosilicate as a silica precursor, and Cr(NO3)(3) as a chromium source. Dehydrogenation of ethane to ethylene (DHE) in the presence of CO2 as soft oxidant was investigated over the Cr-TUD-1 catalyst, which had a nanosponge structure and a surface area of similar to 650 m(2) g(-1), and in which Cr6+ species were dominantly distributed in a form of monochromate. During DHE under N-2, Cr6+ underwent partial reduction to Cr3+ /Cr degrees with concomitant formation of large-sized Cr2O3 and CrCx particles. As a result, the Cr-TUD-1 catalyst was deactivated within 2 h due to both the diminish of chromium active sites and the formation of coke. Replacement of N-2 with CO2 enhanced the catalyst stability and produced little coke, which was attributed to enhanced inter-convertibility of Cr6+ and highly dispersed Cr3+ and a reverse Boudouard reaction between coke and CO2. Aggregated large Cr2O3 nanoparticles could not be readily oxidized to Cr6+ by CO2. The addition of O-2 to CO2 further enhanced catalyst lifetime because the oxygen contributed to the redispersion of sintered Cr2O3 nanoparticles to form isolated Cr6+ species.