Role of phosphorus (P) additive in the performance of char-supported nickel (Ni) catalyst on tar reforming

Abstract

Developing high-efficiency and low-cost tar removal catalysts is immediate and critical for gasification technology. In this work, phosphorus (P) was introduced into char-supported nickel (Ni) catalysts for steam reforming of tar. P and Ni were loaded on the catalyst support precursor, Yining coal oxidized by 20% H2O2, using two kinds of loading sequence, Ni, P co-loading and stepwise loading to obtain (P + Ni)/20%O-C and P-Ni/20%O-C catalysts respectively. Sand and Ni/γ-Al2O3 were selected for blank experiment and comparison. The self-designed dual-stage quartz reactor was used as an evaluation device to test tar steam reforming activity of the catalysts. Preparation conditions for catalyst and reaction technology were also optimized. The effect of P on the structure and acidity of catalysts was investigated by XRD, N2 adsorption, SEM, TEM, XPS, and NH3-TPD. It was found that (P + Ni)/20%O-C prepared by Ni, P co-loading method exhibited superior catalytic performance due to a better dispersion of Ni, more acid sites and higher amount of Ni0. Meanwhile, it is verified that pH 11 and 600 °C is the optimal preparation condition and reaction temperature. Compared to Ni/γ-Al2O3, the (P + Ni)/20% O-C catalyst achieved the highest reforming gas yield (39.3 mmol/g) and lowest tar yield (4.9%), which could be attributed to the function of conversion heavy tar to light fraction of (P + Ni)/20%O-C catalyst. That means most polycyclic materials cracked to small molecule products.