Surface modification of Ni catalysts with trace Pd and Rh for oxidative steam reforming of methane
Bimetallic catalysts (Pd–Ni and Rh–Ni) were prepared by co-impregnation and sequential impregnation methods to investigate catalytic performance in oxidative steam reforming of methane. These bimetallic catalysts gave high methane conversion even at low W/F such as 0.07 g h/mol. The thermographical observation clearly demonstrated that the catalyst bed temperature was strongly dependent on the preparation method. The bimetallic catalyst prepared from the sequential impregnation method exhibited much higher resistance to hot-spot formation in oxidative reforming of methane. In particular, Pd–Ni catalysts prepared by the sequential impregnation method showed higher resistance to hot-spot formation than monometallic Pd and Ni catalysts, and this can be a synergetic effect of Pd and Ni. Temperature-programmed reduction (TPR) with H2 revealed that the addition of Pd or Rh by a sequential impregnation method greatly promoted the reduction of Ni species. Extended X-ray absorption fine structure (EXAFS) analysis confirmed the formation of Pd–Ni alloy and the preferential location of Pd atoms on the surface of the bimetallic particles over the Pd/Ni catalysts. Surface modification of Ni with Pd by sequential impregnation is effective for promotion of the activity and suppression of hot-spot formation.
Graphical abstractSurface modification of Ni with trace Pd by a sequential impregnation method (Pd/Ni) was more effective for the suppression of hot-spot formation during oxidative steam reforming of methane than that by a co-impregnation method (Pd + Ni), and the formation of surface Pd–Ni alloy is suggested by EXAFS and TPR. The effect of surface modification with Rh was also investigated. Figure optionsDownload full-size imageDownload as PowerPoint slide
Journal: Applied Catalysis A: General - Volume 318, 20 February 2007, Pages 252–264