High Sulfur Tolerance Research Articles

Oxygen vacancy induced A-site ordering of a superior perovskite ferrite anode for solid oxide fuel cells

Introducing pentavalent niobium stabilizes perovskite lattice of ferrites but reduces oxygen vacancy content. While oxygen vacancies are beneficial for gas adsorption, ion diffusion, and catalytic activity in perovskites, this trade-off is a challenge. Herein, by adjusting A-site rare earth/alkaline earth ratio, we synthesize ABO3-structured perovskite oxides Pr0.75Sr0.25Fe0.875Nb0.125O3-δ (PSFN6271) and Pr0.5Sr0.5Fe0.875Nb0.125O3-δ (PSFN4471) and evaluate their electrochemical performance as anodes for solid oxide fuel cells. PSFN4471 undergoes phase transition in reducing environment, from orthorhombic simple perovskite to tetragonal A-site ordered layered perovskite PrSrFe1.75Nb0.25O6-δ (L-PSFN4471), with the exsolution of Fe0 nanoparticles. High performance, superior coking and sulfur tolerance are demonstrated for L-PSFN4471 anode. We reveal that oxygen vacancy formation is the driven force for the A-site ordering of PSFN4471 and study the differences between PSFN6271 and PSFN4471 in physiochemical properties and electrochemical performance. We demonstrate that the L-PSFN4471 is a high-performance and promising SOFC alternative anode with considerable coking and sulfur poisoning resistance.

Ruddlesden-Popper perovskite anode with high sulfur tolerance and electrochemical activity for solid oxide fuel cells

Solid oxide fuel cells (SOFCs) are regarded as attractive electrochemical energy conversion devices owing to their exceptional efficiencies and superb fuel flexibility. However, their widespread implementations are remarkably restricted by the inferior sulfur tolerance of state-of-the-art nickel-based cermet anodes under practical conditions. Herein, a layered NaLaTiO4 (NLTO) perovskite oxide with Ruddlesden-Popper structure is designed as a new anode for SOFCs operating on sulfur-containing fuels. After impregnating NLTO into a samaria-doped ceria (SDC) scaffold, such impregnated nanocomposite anode exhibits high electrochemical activity, sulfur tolerance and stability in H2S-containing fuels due to the polar layered structure, abundant oxygen vacancies, superior surface basicity and water storage capability, leading to the efficient removal of the deposited/adsorbed sulfur on the surface of this nanocomposite anode. The electrochemical activity of the NLTO-based composite anode for fuel oxidation is further improved by adding nickel nanoparticles through impregnation, showing enhanced power outputs and considerable operational stability in H2S-containing fuels. This study provides a new, high-performing and sulfur-resistant anode for SOFCs, which may promote the commercialization of this technology.

Effect of precipitation variables on the performance of CeO2-based catalysts for waste-to-hydrogen

Waste-to-hydrogen technology, a future net-zero energy mix as a clean hydrogen source, is currently a research hotspot. To upcycle waste to high-value chemicals such as hydrogen, it is necessary to study customized catalysts for water-gas shift (WGS) reactions considering waste-derived synthesis gas. Herein, we aimed to enhance the physicochemical properties of CeO2 supported Pt catalysts by controlling the precipitation variables to develop a highly sulfur-tolerant WGS catalyst using waste-derived synthesis gas. The CeO2 support was prepared by the classic precipitation method. During precipitation, the precipitating agent was injected at different methods and rates. In the case of the normal titration method, the KOH solution was injected into the Ce precursor dissolved solution at rates of 5, 20, and 50 mL/min. In the case of the reverse titration method, the Ce precursor dissolved solution was injected into the KOH solution at rates of 5, 20, and 50 mL/min. The as-prepared Pt/CeO2 catalysts were applied to the WGS reaction with 500 ppm H2S. This work demonstrated that the titration method and titration rate affected the oxygen vacancy concentration and the active metal dispersion of the catalysts, respectively. And these properties worked in combination to determine the sulfur resistance of the catalysts. Subsequently, the high sulfur tolerance and catalytic performance of Pt/CeO2 catalyst prepared by normal titration method with the titration rate of 50 mL/min were due to the high Pt dispersion and concentration of oxygen vacancies.

Hydrotalcite-Based Bimetallic PdNi Catalysts with High Sulfur Tolerance for the Hydrogenation of Dicyclopentadiene Resin

Hydrotalcite-Based Bimetallic PdNi Catalysts with High Sulfur Tolerance for the Hydrogenation of Dicyclopentadiene Resin

Sulfur-poisoning on Rh NP but sulfur-promotion on single-Rh1-site for methanol carbonylation

Sulfur poisoning is a severe problem for most noble metal nanoparticle (NP) catalysts, and ppm or ppb levels of sulfur species could result in dramatic activity reduction or even irreversible deactivation. Developing catalysts with high sulfur tolerance is crucial, yet challenging. Here, we reported a clear discovery in methanol carbonylation that sulfur poisoned the Rh NP (Rh/CMK-3) but promoted the single-Rh1-site (Rh1/AC) while the Rh NP (Rh/AC) experienced a process of atomic dispersion. Strong adsorption of sulfur and the formation of the Rh-S passivation layer were supposed to lead to Rh/CMK-3 sulfur poisoning. However, the detrimental H2S transformed into CH3SCH3 and CH3SH on Rh1/AC and then acted as a ligand of Rh atoms, participating in the subsequent reaction, lowering the energy barrier of the rate-determining step, and lastly promoting the reaction. This work provides benefits in solving the sulfur poisoning of metal NP and developing high sulfur tolerant single-metal-site catalysts.

ZSM-5 core–shell structured catalyst for enhancing low-temperature NH3-SCR efficiency and poisoning resistance

By constructing core–shell ZSM-5@CeO2 support rather than bulk phase for loading copper, the enhanced NH3-SCR performance as well as H2O and SO2 tolerance was achieved. Cu/(ZSM-5@CeO2) catalyst exhibited the superior activity with the lowest T90 at 215 °C, which is due to the interaction between CeO2 shell and copper ions that promotes the redox properties as evidenced by oxygen isotopic exchange technique. The ZSM-5 core provides more acid sites to improve the ammonia adsorption. Thus, the highest activity of Cu/(ZSM-5@CeO2) catalyst can be ascribed to the synergistic effect of redox ability and acidity. The CeO2 shell can react with SO2 preferentially and lead to a high sulfur tolerance. This study provides a strategy for design and the practical applications of NH3-SCR zeolite catalysts.

Sulfur poisoning of La(Ni0.6Fe0.4)O3 cathode material for solid oxide fuel cells

Sulfur poisoning of cathode materials is one of the important factors to cause cathode performance degradation resulting in shortening lifetime of SOFC. The sulfur attacks alkali earth components of the rare earth-transition metal perovskite oxides, such as Ba, Ca, Sr, which reacts with SO2 to form sulfates. In this work, the La(Ni0.6Fe0.4)O3 (LNF) cathode material without alkali earth elements was employed to investigate the sulfur poisoning behavior by flowing 30 ppm SO2 at different temperatures of 500 °C–800 °C. It was found that SO2 readily reacts with the La2O3 component in LNF to form La2O2SO4 at 700 °C and 800 °C. The extent of the chemical reaction is temperature dependent. These results confirm that sulfur poisoning also occurs in cathode materials free of alkali earth components. The study prompts the exploration of new materials and new strategies for the developing new cathode materials with high sulfur tolerance.

Highly sulfur tolerant and regenerable Pt/CeO2 catalyst for waste to energy

Water-gas shift reaction was applied to upcycle a waste-derived synthesis gas, which contains sulfur as an impurity. Pt/CeO2 was chosen as an appropriate catalyst through a metal and support screening study. The Pt/CeO2 catalyst showed stable catalytic activity without any deactivation for 100 h when the H2S was injected to 100 ppm, and still showed a sulfur tolerance even after 1,000 ppm of H2S was injected. In particular, the catalytic activity was fully regenerated when the H2S injection was stopped, regardless of the H2S concentration. The high sulfur tolerance and regeneration rate of Pt/CeO2 catalyst was due to the high oxygen storage capacity. This accelerates the redox mechanism of the water-gas shift reaction, and also helps the removal of the adsorbed sulfur on the Pt through the oxidation reaction with the mobile oxygen originated from the CeO2.

A theoretical study of sulfur poisoning tolerance at the interface of Mo doped Ni/Yttria-Stabilized Zirconia

Sulfur poisoning is a crucial problem for solid oxide fuel cell (SOFC) anode leading to increasing research works on the development of the anode materials with high sulfur tolerance. By the first principle calculations of hydrogen sulfide dissociation and sulfur atoms diffusion at the interface between the Ni or Mo-doped-nickel and Yttria-Stabilized Zirconia (YSZ), we find that Mo-doped-Ni/YSZ anode not only increases the hydrogen sulfide dissociation barriers, but also increases the barriers of the sulfur diffusion to the oxygen vacancy at the interface of Ni and YSZ, especially for YSZ in oxygen enriched conditions. Here we offer a new theoretical study of Mo-doped-Ni/YSZ sulfur poisoning tolerance at the interface.

Fluorine functionalized graphitic carbon nitride for cataluminescence sensing of H2S

Abstract Graphitic carbon nitride, as an excellent metal-free catalyst, is a promising candidate for cataluminescence (CTL) sensing of H2S owing to its high sulfur tolerance, environmental friendliness and low cost. Herein, in view of inner chemical inertness and low special surface area of g-C3N4, fluorine with strong electronegativity was employed to adjust the electron density of g-C3N4 to obtain fluorine functionalized graphitic carbon nitride (F-g-C3N4) for H2S sensing. As expected, the CTL response of F-g-C3N4 exhibits more than 30 times higher towards H2S by contrast with that of g-C3N4. Results demonstrated that F-g-C3N4 was more conducive to the adsorption of O2 and H2S due to the enlarged special surface area, the easier formation of hydrogen bond and the changed electronic structure, which was also supported by density functional theory calculations. Additionally, the F-g-C3N4-based sensor exhibits as high sensitivity as that of metal catalyst-based sensors but a longer lifetime. Meanwhile, the F-g-C3N4-based sensor has much higher CTL responses in the range of 1.27∼64.00 μg mL−1, lower detection limit of 0.07 μg mL−1 when comparing with previously reported metal-free catalyst-based sensors. Undoubtedly, this work not only opened up a novel approach to improve the sensing performance of g-C3N4, but also proposed an efficient strategy for obtaining satisfying catalytic performance of other metal-free layered materials.

Pulverizing Fe2O3 Nanoparticles for Developing Fe3C/N‐Codoped Carbon Nanoboxes with Multiple Polysulfide Anchoring and Converting Activity in Li‐S Batteries

AbstractSluggish redox kinetics, shuttle effect, poor conductivity, and large volume change of sulfur limit the practical applications of lithium‐sulfur batteries. Hollow, porous, and necklace‐like Fe3C/N‐codoped carbon nanoboxes (Fe3C/NC) connected by N‐doped carbon (NC) nanofibers are designed by pulverizing Fe2O3 embedded in polyacrylonitrile (PAN) fibers to produce multifunctional sulfur hosts, which exhibit multiple polysulfide anchoring and catalytic conversion activities. Experimental and first‐principles density functional theory studies reveal that the uniformly distributed Fe3C and N units in the nanoboxes can significantly suppress the polysulfide shuttle effect. The conversion of polysulfides (LiPSs) to Li2S is catalyzed during discharge. The process relies on the fast electron transfer through the NC nanofibers and facilitated Li+ diffusion through the porous nanobox shells. The structural characteristics (“boxes in fibers”) of the nanoboxes influence the high sulfur loading and tolerance of volume variation of LiPSs, resulting in the synergistic catalysis of the redox reactions. A high capacity of 645 mAh g−1 after 240 cycles at 1 C, a high capacity of 712 mAh g−1 at a high sulfur loading of 5 mg cm−2 after 100 cycles at 0.2 C, and an enhanced areal capacity of 3.6 mAh cm−2 are demonstrated.

A-site defects in LaSrMnO3 perovskite-based catalyst promoting NOx storage and reduction for lean-burn exhausts

Herein, we report the high De-NOx performance of the A-site defective perovskite-based Pd/La0.5Sr0.3MnO3 catalyst. The formation of the defective perovskite structure can be proved by both the increased Mn4+/Mn3+ ratio and serious lattice contraction due to cationic nonstoichiometry. It promotes the Sr doping into perovskite lattice and reduces the formation of the SrCO3 phase. Our results demonstrate that below 300 °C the A-site defective perovskite can be more efficiently regenerated than the SrCO3 phase as NOx storage sites due to the latter's stronger basicity, and also exhibits the higher NO oxidation ability than the A-site stoichiometric and excessive catalysts. Both factors promote the low-temperature De-NOx activity of the Pd/La0.5Sr0.3MnO3 catalyst through improving its NOx trapping efficiency. Nevertheless, above 300 °C, the NOx reduction becomes the determinant of the De-NOx activity of the perovskite-based catalysts. A-site defects can weaken the interactions between perovskite and Pd, inducing activation of Pd sites by in-situ transformation from PdO to metallic Pd in the alternative lean-burn/fuel-rich atmospheric alternations, which boosts the De-NOx activity of the Pd/La0.5Sr0.3MnO3 catalyst. The Pd/La0.5Sr0.3MnO3 catalyst exhibits the high sulfur tolerance as well. These findings provide insight into optimizing the structural properties and catalytic activities of the perovskite-based catalysts via tuning formulation, and have potential to be applied for various related catalyst systems.

Review of Researches on SCR Catalyst with Low Temperature and high Sulfur Tolerance and Theoretical Design

Selective catalytic reduction (SCR) of nitrogen oxides (NOx) using ammonia (NH3) is currently the main technology for flue gas denitration. However, the currently widely used commercial catalysts (such as V2O5-WO3 / TiO2, V2O5-MoO3 / TiO2, etc.) have the disadvantages of high operating temperature, narrow active temperature window, and high catalytic cost. Therefore, in recent years, researchers have devoted themselves to the development of low-cost and efficient low-temperature SCR catalytic materials. This paper summarizes the research progress of low-temperature (less than 250 °C) selective catalytic reduction of NOx by unsupported metal oxide catalysts, supported metal oxide catalysts, precious metals, and molecular sieve catalysts. Among them, manganese-based catalysts show good low-temperature selectivity and stability, and have good application prospects. Finally, the research directions of manganese low temperature SCR catalysts are prospected and theoretically designed based on the existing problems.

Hydroconversion of Aromatic Hydrocarbons over Bimetallic Catalysts

Bimetallic catalysts (BMC) for hydroconversion of aromatic hydrocarbons (ArH) have been designed by modification of Ni/Al2O3 with chromium(0) compounds and phosphoromolybdic heteropolyacid (HPA). Catalysts were tested in hydrogenation of benzene and toluene, in hydrodemethylation of pure toluene and they were shown to possess a high activity, selectivity and sulfur tolerance under conditions of the processes above. The activity of BMC in these processes was much higher as compared with that of two-component (Ni-Cr, Ni-HPA) or conventional Ni/Al2O3 catalysts. Using BMC, hydrogenation of benzene and toluene proceeds with activity increased (up to 34–38 mol/kg·h) and toluene hydrodemethylation may be performed with improved selectivity (90.3%) and benzene yield (81%). The high sulfur tolerance of BMC was demonstrated by performing hydrodemethylation of toluene containing up to 500 ppm S.

Manganese-cerium mixed oxides supported on rice husk based activated carbon with high sulfur tolerance for low-temperature selective catalytic reduction of nitrogen oxides with ammonia.

A rice husk-derived activated carbon supported manganese–cerium mixed oxide catalyst (Mn–Ce/RAC) was prepared by an impregnation method and tested for the selective catalytic reduction of nitrogen oxides with ammonia (NH3-SCR). 5 wt% Mn–Ce/RAC catalyst showed the highest activity, yielding nearly 100% NOx conversion and N2 selectivity at 240 °C at a space velocity of 30 000 h−1. Compared with commercial activated carbon supported manganese–cerium mixed oxide catalyst (Mn–Ce/SAC), a higher SCR performance with good SO2 tolerance could be observed in the tested temperature range over the Mn–Ce/RAC catalyst. The characterization results revealed that the Mn–Ce/RAC catalyst had a higher Mn4+/Mn3+ ratio, amount of chemisorbed oxygen and more Brønsted acid sites than the Mn–Ce/SAC catalyst. The XRD analysis indicated that Mn–Ce oxides were highly dispersed on the RAC support. These properties of Mn–Ce/RAC assisted the SCR reaction. Moreover, in situ DRIFTS results demonstrated that sulfate species formation on Mn–Ce/RAC was much less in the presence of SO2 than that of Mn–Ce/SAC, which might be ascribed to the reduced alkalinity of the catalyst by the presence of SiO2 in RAC.

Ag monolayer doped by Pt atom on WC (0001) surface: A good catalyst for H2 dissociation with high sulfur tolerance

H2 dissociation barriers on Ag (111), Ag monolayer on WC (0001) (AgML/WC), Ag monolayer doped by Pt atom on WC (0001) (AgMLPt-d/WC) surface are decreasing from 1.07 to 0.03 eV. The ab initio atomistic thermodynamic data shows that at typical planar SOFC operating temperatures of 923–1073 K, under 100000-ppm pH2S/pH2, AgMLPt-d/WC can be sulfur free clean surface. Therefore, compared with traditional Nickel/Yttria-stabilized zirconia (Ni/YSZ) Solid Oxide Fuel Cells (SOFCs) anode, AgMLPt-d/WC shows high activity towards H2 dissociation and high tolerance of sulfur poisoning.

Catalytic Activities of Noble Metal Phosphides for Hydrogenation and Hydrodesulfurization Reactions

In this work, the development of a highly active noble metal phosphide (NMXPY)-based hydrodesulfurization (HDS) catalyst with a high hydrogenating ability for heavy oils was studied. NMXPY catalysts were obtained by reduction of P-added noble metals (NM-P, NM: Rh, Pd, Ru) supported on SiO2. The order of activities for the hydrogenation of biphenyl was Rh-P > NiMoS > Pd-P > Ru-P. This order was almost the same as that of the catalytic activities for the HDS of dibenzothiophene. In the HDS of 4,6-dimethyldibenzothiophene (4,6-DMDBT), the HDS activity of the Rh-P catalyst increased with increasing reaction temperature, but the maximum HDS activity for the NiMoS catalyst was observed at 270 °C. The Rh-P catalyst yielded fully hydrogenated products with high selectivity compared with the NiMoS catalyst. Furthermore, XRD analysis of the spent Rh-P catalysts revealed that the Rh2P phase possessed high sulfur tolerance and resistance to sintering.

The mechanism of the high resistance to sulfur poisoning of the rhenium doped nickel/yttria-stabilized zirconia

The structural stability of the Ni4 and Ni4−xRex clusters on the yttria-stabilised zirconia (YSZ) surfaces under sulfur adsorption is systematically studied using a first-principles method based on density functional theory. It is found that the Ni4−xRex alloy cluster is more difficult to deform under sulfur adsorption than the pure Ni4 cluster on the YSZ(1 1 1) surfaces. The results are helpful for explaining why Ni alloyed with Re is more tolerant for sulfur poisoning and provide guidance for designing Ni-based catalyst with high sulfur tolerance.

Density functional theory study for the enhanced sulfur tolerance of Ni catalysts by surface alloying

Sulfur compounds in fuels deactivate the surface of anode materials in solid oxide fuel cells (SOFCs), which adversely affect the long-term durability. To solve this issue, it is important to design new SOFC anode materials with high sulfur tolerance. Unfortunately, it is difficult to completely replace the traditional Ni anode owing to its outstanding reactivity with low cost. As an alternative, alloying Ni with transition metals is a practical strategy to enhance the sulfur resistance while taking advantage of Ni metal. Therefore, in this study, we examined the effects of transition metal (Cu, Rh, Pd, Ag, Pt, and Au) doping into a Ni catalyst on not only the adsorption of H2S, HS, S, and H but also H2S decomposition using density functional theory (DFT) calculations. The dopant metals were selected rationally by considering the stability of the Ni-based binary alloys. The interactions between sulfur atoms produced by H2S dissociation and the surface are weakened by the dopant metals at the topmost layer. In addition, the findings show that H2S dissociation can be suppressed by doping transition metals. It turns out that these effects are maximized in the Au-doped Ni catalyst. Our DFT results will provide useful insights into the design of sulfur-tolerant SOFC anode materials.

(Invited) Sulfur Poisoning of Ni-Based SOFC-Anodes – Short and Long Term Behavior

Solid Oxide Fuel Cells (SOFCs) are affected by sulfur compounds contained in almost all available fuels. Even small amounts of sulfur in the ppm range can decrease the performance of SOFCs. In this contribution the impact of sulfur on the durability of Ni-based cermet anodes will be discussed. Different Ni/ceria cermet anodes were tested with respect to their sulfur tolerance. Impedance analysis of single cells exhibiting such anodes revealed a significantly improved sulfur tolerance. The best performance with an initial polarization resistance below 200 mW×cm² was achieved by infiltrating a Ni/CeO2 coating. The high sulfur tolerance of such anodes seems to be attributed to the large amount of Ni/ceria triple phase boundaries. A durability test of an anode supported cell with Ni/zirconia cermet anode and Ni/CeO2 coating was performed. The test revealed a good initial performance but a strong degradation of the polarization resistance.