Optimization of MxOy (La2O3 or Gd2O3) content in Rh/MxOy-Al2O3 catalyst formulation for the propane steam reforming reaction

Abstract

Heading full speed towards the extensive use of H2 for humanity's energy needs, blue hydrogen production from light hydrocarbons is one of the most promising alternatives. In this study the production of hydrogen through propane steam reforming (PSR) reaction is investigated over Rh nanoparticles dispersed on MxOy-Al2O3 supports of variable MxOy (M: La, Gd) content towards optimizing catalytic performance. The intrinsic activity and the formation of intermediate CH4 are markedly affected by varying MxOy content passing through a maximum for 10 wt% La2O3 or Gd2O3. Up to 8- and 3.5-fold increases in turnover frequency (TOF) at 400 °C are achieved on these optimally loaded with La2O3 and Gd2O3 catalysts, respectively, accompanied by more than two-fold higher H2 yields. The reducibility of both rhodium species and the MxOy-Al2O3 support strongly depends on the MxOy content, which then determines the catalytic activity. In situ diffuse reflectance infrared furrier transform spectroscopy (DRIFTS) experiments revealed that CHx species generated by the dissociative adsorption of propane interact either with H2 yielding CH4 and/or with hydroxyl groups producing formate species and eventually COx and H2 in a manner which depends on MxOy content. However, the latter path is over-favored for samples with 20 wt% MxOy possessing excessive reducibility, and in combination to an over-strengthening of formates adsorption, the conversion rate to COx and H2 is strongly inhibited. Scaling-up the fabrication of the most active Rh/10%La2O3-Al2O3 catalyst at higher application readiness (structured as pellets) and testing under realistic conditions revealed its suitability for propane reformers.