Fe and CaO promoted Ni catalyst on gasifier bed material for tar removal from producer gas

Abstract

A new Ni-based mixed oxide material (Ni-Fe-CaO) for catalyzing Carbo HSP gasifier bed material was prepared and characterized by XRD, TPR, TEM, and SEM techniques. The catalyst performance for tar removal from a simulated producer gas mixture via steam reforming was tested in a laboratory-scale fixed-bed reactor between 700 and 800°C, using toluene and ethylene as tar surrogates. Ni–Fe–CaO catalysts had significantly higher activity and deactivation resistance for toluene removal compared to either Ni–Fe or Ni catalysts. Keeping CaO loading similar in the catalysts, the Ni:Fe ratio was varied and the optimum tar conversion and highest COx selectivity were obtained with ratios of 3:1 and 2:1. The turn over frequency (TOF) on Ni in the Ni–Fe–CaO mixed oxides were higher compared to pure Ni or Ni–CaO combinations and increased with lowering Ni/Fe ratio. High tar removal activity (80% vs 68%) and COx selectivity (96% vs 98%) at 750°C were obtained for 1.6% (Ni45Fe15Ca40)/Carbo HSP and 1.6% (Ni40Fe20Ca40)/Carbo HSP compositions, respectively. Deactivation occurred mainly due to sintering of the 1.6% (Ni45Fe15Ca40) composition reducing conversion efficiency by 17% (from 99.7% to 83%) after 48h in time-on-stream at 800°C. After regeneration with a O2/H2 sequence, the conversion was reduced from 98% to 80% after 24h in time-on-stream. Similarly, 1.6% (Ni40Fe20Ca40) composition shows a stable conversion of ∼80% at the end of 50h, which was much superior compared to the 1% (Ni65Fe35)/Carbo HSP catalyst. The individual role of Fe and CaO in promoting Ni for improving catalytic activity and stability in Ni-Fe-CaO was investigated