Effect of Pd and Rh promotion on Ni/Al2O3 for NO reduction by hydrogen for stationary applications

Three Ni based catalysts, Ni(10 wt.%)/Al2O3, Ni(10 wt.%)-Pd(0.5 wt.%)/Al2O3, and Ni(10 wt.%)-Rh(0.5 wt%)/Al2O3, were comparatively tested in the catalytic reduction of NO by hydrogen. Catalytic activity tests consisted in temperature programmed reactions (TPRea) under plug flow conditions, in the 50-350 degrees C temperature range, with a rate of 5 degrees C/min. The feed stream corresponded to a reactant ratio of NO:H-2 = 1:1.3 and a GHSV of 4500 h(-1). Catalytic activity results proved that promotion with low concentrations of both Pd and Rh increases the catalytic performances of the Ni based catalyst, in respect to NO conversion, N-2 selectivity and N-2 yield. By far, the most efficient catalyst in the NO + H-2 reaction proved to be Ni-Pd/Al2O3, with NO conversions greater than 95% and N-2 selectivity of at least 90% at T >= 100 degrees C. Stability tests confirmed the Pd promoted catalyst as the most efficient one in the investigated series. The catalytic performance in terms of N-2 selectivity/yield for the Ni-Rh/Al2O3 catalyst proved to be only slightly superior to that corresponding to Ni/Al2O3, although both Ni and Rh are efficient in the dissociative adsorption of NO (NO-TPD). The mono- and bimetallic catalysts were characterized by different investigation techniques such as: N-2 adsorption-desorption isotherms at 196 degrees C (BET), X-ray powder diffraction (XRD), temperature programmed reduction (TPR), temperature programmed desorption of hydrogen (H-2-TPD) and NO (NO-TPD). Characterization techniques revealed that promotion with small amounts of Pd or Rh enhances the reducibility of the supported NiO in the catalyst precursor, as well as the dispersion of the metal on the catalyst surface. (C) 2014 Elsevier B.V. All rights reserved.