Ni supported on bioapatite for WGS: Improving catalyst stability and H2 selectivity by Pt-doping and thermochemical activation of the support

Abstract

Catalytic properties of Ni and NiPt catalysts supported onto naturally derived hydroxyapatite (HAp) were investigated for the Water-Gas Shift (WGS) reaction in the 200–450 °C range. HAp was obtained by thermochemical conversion of waste animal bones which yield a porous solid mainly composed by apatite. A feed composition representative of real reformer outlet stream was used (CO/H2O/CO2/H2 = 5/46/4/31 mol %) at a gas hourly space velocity of 120,000 h−1. The catalysts were thoroughly characterised by N2 physisorption, ICP-AES, H2-chemisorption, XPS, FTIR, SEM-EDX, XRD, H2-TPR, CO2-TPD, and NH3-TPD. From the light-off catalytic tests, it was found that all catalysts reached the equilibrium CO conversion in the 350–400 °C range. Pt doping into pristine Ni/HAp did not enhance neither catalytic activity nor selectivity to hydrogen. Interestingly, thermochemical activation (acid treatment) aimed to reduce the CH4 formation (@ 350 °C) by around two-fold (25 % vs. 9–14 %) with a concomitant increase in the hydrogen yield. Moreover, catalytic stability was also improved. For instance, after 30 h TOS CO conversion dropped by 50 % for the pristine Ni/HAp and only 7 % for NiPt/SHAp catalyst. Similarly, the latter showed the highest and most stable hydrogen yield throughout all the long-term test.