Lattice oxygen mobility and acidity improvements of NiO–CeO2–ZrO2 catalyst by sulfation for NOx reduction by ammonia

Insight into the promoting effect of support pretreatment with sulfate acid on selective catalytic reduction performance of CeO2/ZrO2 catalysts

In this paper, sulfated ZrO₂ were synthesized via precipitation and impregnation method, and the promoting effects of support sulfation on selective catalytic reduction (SCR) performance of CeO₂/ZrO₂ catalysts were investigated. The results revealed that sulfated ZrO₂ could significantly enhance the SCR activity of CeO₂/ZrO₂ catalysts in a wide temperature range. Especially when S/Zr molar ratio was 0.1, CeO₂/ZrO₂-0.1S catalyst exhibited a large operating temperature window of 251 ∼ 500 °C and its N₂ selectivity was 100 % in the temperature range of 150 ∼ 500 °C. Moreover, CeO₂/ZrO₂-0.1S catalyst possessed a superior low-temperature activity over 0.1S-CeO₂/ZrO₂ catalyst. After exposing to 100 ppm SO₂ for 15 h, a high NO conversion efficiency of CeO₂/ZrO₂-0.1S catalyst (90.7 %) could still be reached. The characterization results indicated that ZrO₂ treated with a proper dosage of sulfate acid was beneficial to enlarge the specific surface area greatly. Sulfated ZrO₂ was also in favor of promoting the transformation of CeO₂ from crystalline state to highly-dispersed amorphous state, and inhibiting the transformation of ZrO₂ from tetragonal to monoclinic phase. It could also enhance the total surface acidity greatly with an increase in both Brønsted acid sites and Lewis acid sites, thus significantly improving NH₃ adsorption on catalyst surface. Besides, the promoting effect of support sulfation on SCR performance of CeO₂/ZrO₂ catalysts was also related with the enhanced redox property, higher Ce³⁺/(Ce³⁺+Ce⁴⁺) ratio and abundant surface chemisorbed labile oxygen. The in-situ DRIFTS results implied that nitrate species coordinated on the surface of CeO₂/ZrO₂-0.1S catalyst could participate in the Selective catalytic reduction with ammonia (NH₃-SCR) reactions at either medium or high temperature, suggesting that both Eley-Rideal (E-R) and Langmuir-Hinshelwood (L-H) mechanisms might be followed in SCR reactions.

Gas phase sulfation of ceria-zirconia solid solutions for generating highly efficient and SO2 resistant NH3-SCR catalysts for NO removal

A series of ceria-zirconia solid solutions (Ce_xZr_1-xO₂) were prepared by co-precipitation method and then sulfated with SO₂ + O₂ at 200 °C. Subsequent testing with the selective catalytic reduction of NO by NH₃ (NH₃-SCR) showed that the activity of the sulfated Ce_xZr_1-xO₂ catalysts oxide catalysts exhibited a volcano-type tendency with increasing Zr content. Furthermore, the sulfated Ce_0.6Zr_0.4O₂ catalyst showed the most desirable NH₃-SCR activity at 250-300 °C, and exhibited much better SO₂ resistance at 250 °C. Detailed characterization results demonstrated that Ce_0.6Zr_0.4O₂ could adsorb more surface sulfate species and then produce more stable acid sites than pure CeO₂ at 200 °C. After sulfation treatment, more Ce³⁺ and oxygen vacancies were formed on the surface of Ce_0.6Zr_0.4O₂. In situ diffuse reflectance infrared Fourier transform spectroscopy (in situ DRIFTS) experiments suggested that the nitrates species deposited on the surface of as-prepared Ce_0.6Zr_0.4O₂, which showed no reactivity, could barely deposit on the same sample after sulfation. While, the sulfated Ce_0.6Zr_0.4O₂ had more reactive acid sites to participate in the NH₃-SCR and the reaction proceeded via Eley-Rideal mechanism. This work proved that sulfation treatment could be used in designing an efficient cerium-zirconium based NH₃-SCR catalyst with great application prospect.

A new V2O5–MoO3–TiO2–SO42−nanostructured aerogel catalyst for diesel DeNOxtechnology

A new V₂O₅–MoO₃–TiO₂–SO₄²⁻nanostructured aerogel catalyst exhibits superior SCR activity compared to the V₂O₅–WO₃/TiO₂commercial catalyst (EUROCAT) at high temperatures (375–500 °C).

Investigation of the selective catalytic reduction of NO with NH3 over the WO3/Ce0.68Zr0.32O2 catalyst: the role of H2O in SO2 inhibition

The effect of H₂O and SO₂ on the selective catalytic reduction of NO_x by NH₃ (NH₃-SCR) over WO₃/Ce_0.68Zr_0.32O₂ at 250 °C was systematically investigated using various characterization techniques.

Comparison of support synthesis methods for TiO2and the effects of surface sulfates on its activity toward NH3-SCR

Addition of SO₄²⁻inhibits the transformation of TiO₂from anatase to rutile and generates sulfate salts to increase the surface acidity.

Silver nanoparticles supported on zirconia–ceria for the catalytic wet air oxidation of methyl tert-butyl ether

In this work Ag nanoparticles supported on ZrO₂–CeO₂ promoted with different amounts of CeO₂ were synthesized by deposition–precipitation method in order to test the Catalytic Wet Air Oxidation (CWAO) of Methyl Tert-Butyl Ether (MTBE).

Decomposition behavior of ammonium nitrate on ceria catalysts and its role in the NH3-SCR reaction

Ceria catalyst's redox properties promote NH₄NO₃ decomposition while acidity inhibits this process.

Structure–performance relationships of MnO2 nanocatalyst for the low-temperature SCR removal of NOX under ammonia

To investigate the corresponding relationship between catalytic efficiency and structure, MnO₂ nanomaterials (nanospheres, nanosheets, nanorods) have been prepared successfully, and were thoroughly characterized by SEM and TEM.

Effect of preparation methods on the activity of VOx/CeO2 catalysts for the selective catalytic reduction of NOx with NH3

VO_x/CeO₂ catalysts prepared by a homogeneous precipitation method exhibited high NO_x conversion and strong SO₂ resistance in NH₃-SCR reaction.

NH3-SCR activity, hydrothermal stability and poison resistance of a zirconium phosphate/Ce0.5Zr0.5O2 catalyst in simulated diesel exhaust

A ZP/CZ catalyst exhibited over 80% NO_x conversion at 250–450 °C at a high GHSV of 300 000 h⁻¹ in the presence of H₂O, CO₂ and C₃H₈.

Nb-doped VOx/CeO2 catalyst for NH3-SCR of NOx at low temperatures

The Nb-1VO_x/CeO₂ catalyst exhibited higher NH₃-SCR activity than 3V₂O₅–10WO₃/TiO₂ and also showed excellent SO₂/H₂O resistance.

DRIFT study of CuO-CeO₂-TiO₂ mixed oxides for NOx reduction with NH₃ at low temperatures

A CuO-CeO2-TiO2 catalyst for selective catalytic reduction of NOx with NH3 (NH3-SCR) at low temperatures was prepared by a sol-gel method and characterized by X-ray diffraction, Brunner-Emmett-Teller surface area, ultraviolet-visible spectroscopy, H2 temperature-programmed reduction, scanning electron microscopy and in situ diffuse reflectance infrared Fourier transform spectroscopy (in situ DRIFTS). The CuO-CeO2-TiO2 ternary oxide catalyst shows excellent NH3-SCR activity in a low-temperature range of 150-250 °C. Lewis acid sites generated from Cu(2+) are the main active sites for ammonia activation at low temperature, which is crucial for low temperature NH3-SCR activity. The introduction of ceria results in increased reducibility of CuO species and strong interactions between CuO particles with the matrix. The interactions between copper, cerium and titanium oxides lead to high dispersion of metal oxides with increased active oxygen and enhanced catalyst acidity. Homogeneously mixed metal oxides facilitate the "fast SCR" reaction among Cu(2+)-NO, nitrate (coordinated on cerium sites) and ammonia (on titanium sites) on the CuO-CeO2-TiO2 catalyst at low temperatures.