Applied Catalysis A: General, Vol.480, 108-119, 2014
State of the components of (K)(Ni)W/gamma-Al2O3 catalysts as oxide precursors and after water-gas shift reaction in the presence of sulphur
A W/gamma-Al2O3 system doped with K and/or Ni has been synthesized by consecutive incipient wetness impregnation. The state of the components was characterized by XRD, UV-vis-NIR, XPS, and EPR spectroscopy as well as by means of N-2 physisorption. A variety of surface species was available after calcination, such as monotungstate (-WO4) and polymeric monolayers (-WO6-)(n) with incorporated Ni2+ or K+ ions or more complex Ni-W-O (Al) and K-Ni-W-O-(Al). Presulphided samples were investigated in the water-gas shift (WGS) reaction in presence of sulphur in the feed. In case of H2S-free feed, catalyst deactivation readily occurred. W4+, W5+, and We(6+) oxidation states as well as different sulphur-containing species like paramagnetic sulphur, sulphide sulphur, oxysulphides and sulphate sulphur were registered on the surface after catalytic activity tests with sulphur present in the feed. Both tungsten reducibility and sulphur stability to oxidation represent informative indices related to the catalytic properties of gamma-Al2O3-supported tungsten system, doped with Ni and K, in the WGS reaction. The tricomponent KNiW system exhibited these features to a moderate extent thus leading to its highest catalytic performance that allowed attaining equilibrium values at high temperatures. (C) 2014 Elsevier B.V. All rights reserved.