Mechanism Of Sulfur Poisoning Research Articles

Sulfur poisoning on the La0.75Sr0.25Cr0.5Mn0.5O3-δ-Gd0.1Ce0.9O2-δ fuel electrode for direct electrochemical CO2 reduction in solid oxide electrolysis cells

As a promising energy conversion technology, solid oxide electrolysis cells (SOECs) can efficiently convert CO2 to CO by utilizing renewable energy sources and industrial waste heat. Sulfur poisoning of fuel electrode is a significant drawback to the electrochemical activity and long-term electrolysis performance of SOECs using sulfur-containing fuels. Traditional Ni-based cermet electrodes are susceptible to sulfur poisoning due to the low activation barrier and large enthalpy of the adsorbed sulfur species on the Ni surface. La0.75Sr0.25Cr0.5Mn0.5O3-δ-based materials which exhibit excellent redox stability have been considered as the promising candidates for substitution of Ni-based cermet electrodes. Herein, the sulfur poisoning behavior on the La0.75Sr0.25Cr0.5Mn0.5O3-δ-Gd0.1Ce0.9O2-δ (LSCM-GDC) fuel electrode under CO2–SO2 condition and the mechanism of sulfur poisoning are investigated. The results show that the LSCM-GDC fuel electrode possesses stable electrocatalytic activity as SO2 content up to 10 ppm. With increasing of SO2 content, metallic sulfide, amorphous sulfur and sulfate impurities can be detected on the electrode surface, which decrease the reactive sites and hinder the charge transfer and oxygen ions transport pathway, leading to degradation of the electrolysis performance. The plausible sulfur poisoning mechanism is divided into two categories, namely, thermodynamic and electrochemical processes. For thermodynamic process, SO2 molecules adsorb into oxygen vacancies and couple to coordinated oxygen lattices to form sulfates; for electrochemical process, the formation of amorphous sulfur and metallic sulfide impurities is caused by the binding of SO2 molecules to surface polarons at three phase boundaries under cathodic polarization. This work provides new insights into sulfur poisoning effect on the perovskite oxide electrodes.

Study on the mechanism of sulfur poisoning in toluene catalyzed by Co3O4/γ-Al2O3 sulfur tolerant catalyst containing spinel structure

In this paper, in-situ thermal decomposition of ammonium sulfate method was used to cause sulfur poisoning of Co3O4/γ-Al2O3 catalyst rapidly and quantitatively. The pore structure, valence state of active species, surface morphology and acidity of the catalyst before and after sulfur poisoning were characterized, and its influence on catalytic combustion of toluene was studied. The results showed the crystal shape of the catalyst changed little after sulfur poisoning. As sulfur poisoning gradually deepened, the formation of sulfate blocked the pores, the high-valence cobalt decreased, strong acid sites increased, and its catalytic activity for toluene combustion gradually decreased. Formation of cobalt sulfate was a main reason for the decline in catalyst activity. Spinel phase CoAl2O4 formed outside γ-Al2O3 framework can adsorb a large amount of sulfur species to form sulfate, protecting Co3O4 and delaying the deactivation of catalysts.

Effect of H2S in syngas on the Fischer–Tropsch synthesis performance of a precipitated iron catalyst

The sulfur limit, the relationship between the sulfur added and the surface Fe atoms lost (Fe/S), and mechanism of sulfur poisoning were studied using an iron Fischer–Tropsch synthesis (FTS) catalyst (100 Fe/5.1 Si/2.0Cu/3.0K). The FTS reaction was carried out at 230–270°C, 1.3MPa, H2/CO=0.67–0.77 and 30–70% CO conversion using a 1-L slurry phase reactor. The used Fe catalysts were characterized by XRD, Mössbauer spectroscopy and XANES spectroscopy to understand the deactivation mechanism of the Fe based catalyst after adding up to 1ppm H2S in the feed. Co-feeding of 0.1ppm H2S in syngas for 70h caused a very small change in the activity of the Fe catalyst, but increasing the H2S level to 0.2ppm or above resulted in measurable deactivation of the Fe catalyst over a similar time period. The limit of sulfur level in the syngas feed (sensitivity) was determined to be 50ppb. The added sulfur improved the selectivities of the secondary reactions of olefins and the WGS reaction even though the rates for these declined. The addition of H2S decreased CH4 selectivity and increased C5+ selectivities of the Fe catalyst. The Fe/S ratio, which can be used to define the poisoning ability of sulfur for the iron catalyst, was quantified based on the deactivation data obtained. The Fe/S ratio strongly depended on temperature and decreased remarkably with increasing temperature. At 270°C one sulfur atom was found to eliminate ∼6 surface Fe atoms, and the ratio increased to 7.2 at 260°C and increased further to 13.5 at 230°C. The Fe/S relationship with increasing temperature is in good agreement with sulfur sorption theory. The changes in FTS and WGS rates of the Fe catalyst by sulfur were also studied. The decreases in rates of the two reactions were nearly the same. The results of XRD and Mössbauer spectroscopy indicated that the online addition of sulfur did not greatly alter the distributions of iron carbide and magnetite. Both data sets consistently suggest an adsorption mechanism, in line with the results of reaction testing. XANES results at the S K-edge further confirmed sulfur adsorption, and some sulfide and sulfate species, likely confined to the surface zone, were detected. In this study, the sulfur tolerances of the precipitated Fe and a supported Co catalyst were compared at an identical temperature (i.e., 230°C), and similar M/S ratios (13.5–15.0) were obtained.

ChemInform Abstract: Research on Mechanism of Sulfur Poisoning in the Precious Metal Catalyst

AbstractReview: 14 refs.

Mechanism of Sulfur Poisoning and Storage: Adsorption and Reaction of SO2 with Stoichiometric and Reduced Ceria Films on Cu(111)

We have performed a systematic synchrotron radiation photoelectron spectroscopy (SR-PES) study of the interaction of SO2 with stoichiometric CeO2(111) and reduced CeO2–x films supported on Cu(111). Resonant photoelectron spectroscopy (RPES) was utilized to monitor changes in the cerium oxidation states. Adsorption of SO2 at 150 and 300 K results mostly in formation of sulfite (SO32–) species on both reduced and stoichiometric ceria. Other species such as sulfate (SO42–), SO2 chemisorbed at cationic sites, anionic SO2–, atomic sulfur, surface sulfides, and bulk oxy-sulfides were detected. The origin of these species is discussed in relation to the changes in the oxidation state of ceria cations at the surface. The thermal evolution of the species formed upon adsorption at 150 and 300 K was studied systematically on both the stoichiometric and the reduced films. It was found that the sulfite partially desorbs to release SO2 and partially decomposes. In general, the reduced CeO2–x surface was found to be much more active toward cleavage of S–O bonds, as indicated by a higher amount of oxy-sulfide species produced. The decomposition pathways can be monitored via changes of the ceria oxidation state and are discussed in relation to the stoichiometry of the ceria surface.

Research on Mechanism of Sulfur Poisoning in the Precious Metal Catalyst

In this paper, the research on the catalyst sulfur poisoning in recent years were reviewed, including the reason and mechanism of sulfur poisoning, dynamics for deactivation, recovery and regeneration of catalyst.

Aromatic Reduction Over Supported Modified Platinum Catalysts Influence of a Second Metal on the Sulfur Resistance of Platinum

Pt-M/Al2 O3 bimetallic catalysts with M = Ge , Au or Pd were prepared and characterised by H2 -O2 volumetric titration and IR(CO) spectroscopy. The effects of the second metal on the sulfur resistance of platinum were investigated by the hydrogenation of orthoxylene. Compared to platinum monometallic reference catalyst, the bimetallic catalysts ranking in terms of hydrogenation activity was PtPd > PtAu = Pt >> PtGe . Correlation between these catalysis results and electronic properties extracted from IR(CO), or orthoxylene hydrogenation without sulfur, shows that sulfur resistance of platinum can not be exclusively related to an electronic effect and an electrodeficient character of Pt surface atoms. The mechanism of sulfur poisoning is discussed.

Steric and electronic effects of sulfur on CO adsorbed on Pd(100)

The mechanism of sulfur poisoning was studied on the Pd(100) surface using TPD, HREELS, and LEED for sulfur coverages ranging from zero to saturation (0.5 monolayer). A rapid initial decrease in the CO saturation coverage at 80 K was observed up to a sulfur coverage of about 0.1 ML. Coincident with this coverage decrease the formation of high-density CO compression structures is blocked as revealed by LEED. Thereafter the CO coverage declines linearly in a nearly 1:1 ratio with the addition of adsorbed sulfur. For low θ CO the CO stretching frequency increased from 1895 to 1925 cm −1 as the sulfur coverage was increased from zero to saturation. The CO singleton frequency at θ s=0.50 is slightly less than the reported C 12O singleton stretching frequency in the presence of 0.5 monolayer of C 13O, indicating that adsorbed sulfur has less effect on the CO bond than adsorbed CO itself at this coverage. The observed value of the CO stretching frequency at CO saturation coverage decreases with increasing sulfur coverage. This net decrease in ν(CO) with θ s for saturation coverage by CO coincides with the reduction in CO coverage in the presence of adsorbed sulfur. Sulfur does not appear to change the bridge-site preference of adsorbed CO, and the decrease in the saturation coverage for 0< θ s<0.10 is ascribed to disorder in the CO adlayer induced by the preadsorbed sulfur. When compared to the sulfur-free surface at the same CO coverage there is an increase in the CO stretching frequency. This increase in the CO stretching frequency at saturation coverage by CO due to adsorbed sulfur rises rapidly at low sulfur coverage and remains constant above θ s=0.15. This effect appears to be due to COCO coupling transferring the local changes in frequency caused by sulfur to the entire adsorbed layer.