Chizhong Wang

Improvement of Activity and SO2 Tolerance of Sn-Modified MnOx–CeO2 Catalysts for NH3-SCR at Low Temperatures

The performances of fresh and sulfated MnOx-CeO₂ catalysts for selective catalytic reduction of NOx by NH₃ (NH₃-SCR) in a low-temperature range (T < 300 °C) were investigated. Characterization of these catalysts aimed at elucidating the role of additive and the effect of sulfation. The catalyst having a Sn:Mn:Ce = 1:4:5 molar ratio showed the widest SCR activity improvement with near 100% NOx conversion at 110-230 °C. Raman and X-ray photoelectron spectroscopy (XPS) indicated that Sn modification significantly increases the concentration of oxygen vacancies that may facilitate NO oxidation to NO₂. NH₃-TPD characterization showed that the low-temperature NH₃-SCR activity is well correlated with surface acidity for NH3 adsorption, which is also enhanced by Sn modification. Furthermore, as compared to MnOx-CeO₂, Sn-modified MnOx-CeO₂ showed remarkably improved tolerance to SO₂ sulfation and to the combined effect of SO₂ and H₂O. In the presence of SO₂ and H₂O, the Sn-modified MnOx-CeO₂ catalyst gave 62% and 94% NOx conversions as compared to 18% and 56% over MnOx-CeO₂ at temperatures of 110 and 220 °C, respectively. Sulfation of SnO₂-modified MnOx-CeO₂ may form Ce(III) sulfate that could enhance the Lewis acidity and improve NO oxidation to NO₂ during NH₃-SCR at T > 200 °C.

Substitution of WO3 in V2O5/WO3–TiO2 by Fe2O3 for selective catalytic reduction of NO with NH3

To improve N2 selectivity and lower the cost, WO3 in V2O5/WO3–TiO2 was substituted by a low cost composition Fe2O3 for selective catalytic reduction (SCR) of NO with NH3. The SCR reaction over V2O5/Fe2O3–TiO2 mainly followed the Eley–Rideal mechanism (i.e. the reaction between activated ammonia species and gaseous NO). There were two active components on V2O5/WO3–TiO2 for the activation of adsorbed NH3 (i.e. V5+ and Fe3+). The acid sites on V2O5/Fe2O3–TiO2 mainly resulted from the support Fe2O3–TiO2, so the adsorbed NH3 preferred to be activated by Fe3+ rather than by V5+. V5+ on V2O5/Fe2O3–TiO2 could accelerate the regeneration of Fe3+ on Fe2O3–TiO2 due to the rapid electron transfer between V5+ and Fe2+ on the surface, so the activation of adsorbed NH3 by Fe3+ was promoted. As some NH3 adsorbed on V2O5/Fe2O3–TiO2 was not activated by Fe3+, the inactivated NH3 could then be activated by V5+ on the surface. As a result, 2% V2O5/Fe2O3–TiO2 showed excellent SCR activity, N2 selectivity and H2O/SO2 durability at 300–450 °C. Furthermore, the emission of 2% V2O5/Fe2O3–TiO2 to the fly ash can be prevented by an external magnetic field due to its inherent magnetization. Therefore, 2% V2O5/Fe2O3–TiO2 could be a promising low-cost catalyst in NO emission control.

Design Strategies for P-Containing Fuels Adaptable CeO2–MoO3 Catalysts for DeNOx: Significance of Phosphorus Resistance and N2 Selectivity

Phosphorus compounds from flue gas have a significant deactivation effect on selective catalytic reduction (SCR) DeNOx catalysts. In this work, the effects of phosphorus over three catalysts (CeO2, CeO2-MoO3, and V2O5-MoO3/TiO2) for NH3-SCR were studied, and characterizations were performed aiming at a better understanding of the behavior and poisoning mechanism of phosphorus over SCR catalysts. The CeO2-MoO3 catalyst showed much better catalytic behavior with respect to resistance to phosphorus and N2 selectivity compared with V2O5-MoO3/TiO2 catalyst. With addition of 1.3 wt % P, the SCR activity of V2O5-MoO3/TiO2 decreased dramatically at low temperature due to the impairment of redox property for NO oxidation; meanwhile, the activity over CeO2 and CeO2-MoO3 catalysts was improved. The superior NO oxidation activity contributes to the activity over P-poisoned CeO2 catalyst. The increased surface area and abundant acidity sites contribute to excellent activity over CeO2-MoO3 catalyst. As the content of P increased to 3.9 wt %, the redox cycle over CeO2 catalyst (2CeO2 ↔ Ce2O3 + O*) was destroyed as phosphate accumulated, leading to the decline of SCR activity; whereas, more than 80% NOx conversion and superior N2 selectivity were obtained over CeO2-MoO3 at T > 300 °C. The effect of phosphorus was correlated with the redox properties of SCR catalyst for NH3 and NO oxidation. A spillover effect that phosphate transfers from Ce to Mo in calcination was proposed.

A novel magnetic Fe–Ti–V spinel catalyst for the selective catalytic reduction of NO with NH3 in a broad temperature range

Fe–Ti–V spinel showed excellent SCR activity, N2 selectivity and H2O/SO2 durability at 250–400 °C, and an external magnetic field can effectively prevent the emission of a vanadium based catalyst to the environment due to its magnetization.

Impacts of Pb and SO2 Poisoning on CeO2–WO3/TiO2–SiO2 SCR Catalyst

A CeO2-WO3/TiO2-SiO2 catalyst was employed to investigate the poisoning mechanisms of Pb and SO2 during selective catalytic reduction (SCR). The introduction of Pb and SO2 suppressed the catalytic performance by decreasing the numbers of surface acid and redox sites. Specifically, Pb preferentially bonded with amorphous WO3 species rather than with CeO2, decreasing the numbers of both Lewis and Brønsted acid sites but exerting less influence on the reducibility. SO2 preferentially bonded with CeO2 as sulfate species rather than with WO3, leading to a significant decrease in reducibility and the loss of surface active oxygen groups. Although SO2 provided additional Brønsted acid sites via the interaction of SO42- and CeO2, it had little positive effect on catalytic activity. A synergistic deactivation effect of Pb and SO42- on CeO2 was found. Pb covered portions of the weakly bonded catalyst sites poisoned by SO42-, which increased the decomposition temperature of the sulfate species on the catalyst.

New Insight into SO2 Poisoning and Regeneration of CeO2–WO3/TiO2 and V2O5–WO3/TiO2 Catalysts for Low-Temperature NH3–SCR

In this study, the poisoning effects of SO2 on the V2O5-WO3/TiO2 (1%VWTi) and CeO2-WO3/TiO2 (5%CeWTi) selective catalytic reduction (SCR) catalysts were investigated in the presence of steam, and also the regeneration of deactivated catalysts was studied. After pretreating the catalysts in a flow of NH3 + SO2 + H2O + O2 at 200 °C for 24 h, it was observed that the low-temperature SCR (LT-SCR) activity decreased significantly over the 1%VWTi and 5%CeWTi catalysts. For 1%VWTi, NH4HSO4 (ABS) was the main product detected after the poisoning process. Both of NH4HSO4 and cerium sulfate species were formed on the poisoned 5%CeWTi catalyst, indicating that SO2 reacted with Ce3+/Ce4+, even in the presence of high concentration of NH3. The decrease of BET specific surface area, NO x adsorption capacity, the ratio of chemisorbed oxygen, and reducibility were responsible for the irreversible deactivation of the poisoned 5%CeWTi catalyst. Meanwhile, the LT-SCR activity could be recovered over the poisoned 1%VWTi after regeneration at 400 °C, but not for the 5%CeWTi catalyst. For industrial application, it is suggested that the regeneration process can be utilized for 1%VWTi catalysts after a period of time after NH4HSO4 accumulated on the catalysts.

Facile surface improvement method for LaCoO3 for toluene oxidation

The rational design of low-cost transition metal catalysts that exhibit high activity and selectivity may be the most significant area of investigation in heterogeneous catalysis. A selective dissolution method using acid solutions was previously reported to tune catalyst surfaces. In this work, LaCoO3 (LCO-0) perovskite catalysts were synthesized by the traditional citrate sol–gel method for toluene oxidation. The catalytic activity of the LaCoO3 treated with acetic acid (LCO-1) was significantly increased: the T90 of LCO-1 was 223 °C, which was 40 °C lower than that of the untreated catalyst (LCO-0) under a weight hourly space velocity (WHSV) of 60 000 mL g−1 h−1. The exposed A-site cations of perovskite were slightly etched, but still preserved the original framework according to XRD, TEM, SEM and ICP results. Moreover, LCO-1 exhibited excellent stability even after 500 °C calcination. The high catalytic performance was mainly associated with improvements in reducibility, surface oxygen vacancies and surface area. The high stability was due to the preservation of the perovskite structure after acetic acid treatment.

Selective Catalytic Reduction of NO x with Ammonia over Copper Ion Exchanged SAPO-47 Zeolites in a Wide Temperature Range

Copper‐exchanged H‐SAPO‐47 zeolites were synthesized by an aqueous solution ion exchange method and applied in the selective catalytic reduction of NO with NH3 (SCR). The microporous chabazite (CHA) structure of the catalysts was characterized and confirmed using synchrotron X‐ray diffraction and nitrogen adsorption–desorption experiments. The synthesized Cux‐SAPO‐47 catalysts exhibited excellent SCR activity and nearly 100 % N2 selectivity in a wide temperature range. The Cu0.1‐SAPO‐47 sample exhibited higher activity than the other samples below 250 °C. The weak Lewis acid sites originating from the introduction of Cu2+ were more active than the Brønsted acid sites of the zeolites framework at low temperature. Two types of isolated Cu2+ species with different coordination surroundings were found, namely, Cu2+ cations bonded with the six‐membered rings and those bonded in the CHA cages. The former species exhibited good stability and activity at high temperature, whereas the latter ones were more active at low temperature. The Cu0.1‐SAPO‐47 catalyst provided a considerable amount of isolated Cu2+ bonded in the CHA cages. These results indicated that active Lewis acid sites and isolated Cu2+ species are responsible for their excellent SCR activity.

Promotion Effect of Ga−Co Spinel Derived from Layered Double Hydroxides for Toluene Oxidation

Considering the radius similarity of Al3+ (0.50 Å) and Ga3+ (0.62 Å), Al−Co and Ga−Co layered double hydroxides (LDH) was prepared as precursor to improve the synergetic interaction of the transition metals. The Al−Co and Ga−Co spinel catalysts were obtained by the following calcination for the toluene oxidation. The Ga−Co (Ea=79.5 kJ mol−1) showed higher activity than the Al−Co (Ea=95.4 kJ mol−1), and it exhibited excellent stability and resistance to carbon deposition during a 50 h reaction period at 300 °C. Characterization results indicated that the improved activity of Ga−Co spinel could be attributed to the higher reducibility (H2‐TPR), more surface Co3+ and adsorbed oxygen in quantity (XPS) and adsorbed toluene (Toluene‐TPD) than Al−Co spinel. Compared with traditional Ga−Co binary catalyst, the spinel structure possessed more B‐sites cations outermost of the surface and surface oxygen vacancies for the toluene adsorption and ring‐open reaction.

Solar-Hydrogen Energy System Design

Solar energy is a kind of unstable energy source as its time and the geographical distribution. Thus storage and transportation of solar energy is necessary. An ideal way of doing this is to storage electricity from solar in form of hydrogen which obtained by eletrolysing water. Hydrogen is a energy carrier in a carbon-free, natural cycle. Hydrogen is a fuel which can be transported over long distances and stored so that solar energy can be transported from solar rich area over long distances in pipeline to East of China, stored underground or in containers and used in gaseous or liquid form in industry, households, power stations, motor cars and aviation.