Ni supported on bioapatite for WGS: Improving catalyst stability and H2 selectivity by Pt-doping and thermochemical activation of the support
Unai Iriarte‐Velasco, M.A. Gutiérrez–Ortiz, A.J. Reynoso, J.L. Ayastuy
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.