A comparison of H2S, SO2, and COS poisoning on Ni/YSZ and Ni/K2O-CaAl2O4 during methane steam and dry reforming

Abstract

Research Highlights: The impact of sulfur poisoning by H 2 S, SO 2 , and COS on methane steam and dry reforming over Ni/YSZ and Ni/K 2 O-CaAl 2 O 4 was measured. Ni/YSZ has 15 times lower active nickel surface area than Ni/K 2 O-CaAl 2 O 4 as measured by hydrogen uptake. Ni/YSZ is essentially completely deactivated while Ni/K 2 O-CaAl 2 O 4 maintains some activity for the same time on stream. For both catalysts, the deactivation rates by H 2 S and SO 2 are comparable, while that for COS is much higher. These results suggest the fuel stream for a solid oxide fuel cell must be cleaned to subppm sulfur levels if Ni/YSZ is the anode material and internal methane reforming is desired. Abstract A systematic comparison of sulfur poisoning on Ni/YSZ and Ni/K 2 O−CaAl 2 O 4 , a commercially available reforming catalyst, demonstrated the heightened and rapid degradation of Ni/YSZ methane reforming activity. Ni/K 2 O−CaAl 2 O 4 has nearly 15 times the hydrogen uptake capacity of Ni/YSZ which implies a difference in active nickel area. Because of this difference in active nickel surface area, Ni/K 2 O−CaAl 2 O 4 was diluted in pure α-Al 2 O 3 to achieve the same active nickel surface area as Ni/YSZ. The turnover frequencies (TOF) for steam methane reforming without sulfur on Ni/YSZ and Ni/K 2 O−CaAl 2 O 4 were similar, although there was some deactivation on Ni/K 2 O−CaAl 2 O 4 possibly as a result of coking which was observed visually. Sulfur deactivation on both catalysts was examined for H 2 S, SO 2, and COS at concentrations of 1, 3, and 5 ppm. Ni/YSZ deactivated rapidly to an activity close to zero. Ni/K 2 O−CaAl 2 O 4 deactivated quickly in the first 20 minutes, but then reached a non-zero steady state activity. The relative deactivation rates for the sulfur species examined were COS > SO 2 ≥ H 2 S. Reaction temperatures of 650 • C, 750 • C, and 800 • C were evaluated, but temperature did not strongly affect deactivation rates strongly for either catalyst. The overarching result of this study is that Ni/YSZ methane reforming activity is more sensitive to sulfur deactivation than a commercial reforming catalyst. The effect is so strong, that the use of Ni/YSZ with any hydrocarbon fuel may require removal of sulfur to sub-ppm levels.

Catalyst Deactivation and Regeneration Processes in Biogas Tri-Reforming Process. The Effect of Hydrogen Sulfide Addition

“…As has been reported by other authors, the deactivation by sulfur can be described by the following general reaction Equation (8) [32,33], which is proposed to operate at high temperature:…”

Synergistic effects of sulfur poisoning and gas diffusion on polarization loss in anodes of solid oxide fuel cells

“…Typical concentrations of sulfur impurity are in the range of 5–500 ppm for natural gas and 200–20,000 ppm for biogas . Experiments have shown that the tolerance of Ni‐based anode is below 5 ppm H 2 S at 950–1000°C .…”

“… and are the partial pressures of H 2 S and H 2 in the activation layer. and are calculated through the Hertz‐Knudsen equation with the sticking probability, , where is the sticking probability and …”

Process intensification in the catalytic conversion of natural gas to fuels and chemicals

“…Sulfur reactivity with other metal catalysts is generally ordered as Ni [52] . Sulfur poisoning can be severe, meaning very low levels (e.g., ≤ 1 ppm) can severely reduce the catalytic activity [53][54][55] . Because sulfur is prevalent in petroleumand bio-derived fuels, understanding and controlling sulfur-catalyst interactions is important.…”