Activity and characterization of Ce–Mo–Ti mixed oxide catalysts prepared by a homogeneous precipitation method for selective catalytic reduction of NO with NH 3

Self-doping synthesis of nano-TiO2 with outstanding antibacterial properties under visible light

Nano-TiO2 photocatalysis technology has attracted wide attention because of its safety, nontoxicity and long-lasting performance. However, traditional nano-TiO2 has been greatly limited in its application because its wide band gap can only be activated by ultraviolet light (λ < 387 nm). In this paper, nano-TiO2 was prepared by self-doping method. The synthesized nano-TiO2 was a single anatase crystal type with a particle size of 10 nm and uniform size. In addition, nano-TiO2 has high stability and good dispersion. More importantly, nano-TiO2 exhibits excellent visible light (400-780 nm) activity due to the decrease of bandgap from 3.20 eV to 1.80 eV (less than 2.0 eV) and the presence of a large number of hydroxyl groups on the surface of the nanoparticles. In the antibacterial test, the antibacterial rate of both E.coli and S.aureus was close to 100 % under the irradiation of household low-power LED lamps, showing excellent antibacterial performance, indicating that the prepared nano-TiO2 has broad application prospects in the field of bactericidal and bacteriostatic.

Insight into the reaction mechanism over PMoA for low temperature NH3-SCR: A combined In-situ DRIFTs and DFT transition state calculations

Phosphomolybdic acid catalyst (PMoA/TiO₂) is a promising catalyst for selective catalytic reduction of NO_x with NH₃ (NH₃-SCR) due to its strong acidity and excellent redox property. This work presents the NH₃-SCR reaction mechanism by In-situ diffuse reflectance Infrared Fourier Transform Spectroscopy (In-situ DRIFTs) and density functional theory (DFT). In-situ DRIFTs results indicated that the NH₃-SCR performance over PMoA/TiO₂ followed both Eley-Rideal (E-R) and Langmuir-Hinshelwood (L-H) mechanisms. The reaction pathway, intermediate, transition state and energy barrier over PMoA to complete NH₃-SCR reaction were calculated by DFT. The results showed that the catalytic cycle includes foundational reaction (NH₃ + NO reaction) and regenerative reaction (NH₃ + NO₂ reaction). NH₂, NH₂NO, HNNOH and HO₂NNH species were the key intermediates. In the foundational reactions, NO₂ played an important role in the removal of remaining H atoms. The NH₃ dissociation on Lewis acid site, the internal hydrogen transfer on Brønsted acid site and the formation of HO₂NNH species were the rate-controlling steps. The catalytic cycle of NH₃-SCR over PMoA consists of standard SCR and fast SCR.

Preparation and Performance of Cerium-Based Catalysts for Selective Catalytic Reduction of Nitrogen Oxides: A Critical Review

Selective catalytic reduction of nitrogen oxides with NH3 (NH3-SCR) is still the most commonly used control technology for nitrogen oxides emission. Specifically, the application of rare earth materials has become more and more extensive. CeO2 was widely developed in NH3-SCR reaction due to its good redox performance, proper surface acidity and abundant resource reserves. Therefore, a large number of papers in the literature have described the research of cerium-based catalysts. This review critically summarized the development of the different components of cerium-based catalysts, and characterized the preparation methods, the catalytic performance and reaction mechanisms of the cerium-based catalysts for NH3-SCR. The purpose of this review is to highlight: (1) the modification effect of the various metal elements for cerium-based catalysts; (2) various synthesis methods of the cerium-based catalysts; and (3) the physicochemical properties of the various catalysts and clarify their relations to catalytic performances, particularly in the presence of SO2 and H2O. Finally, we hope that this work can give timely technical guidance and valuable insights for the applications of NH3-SCR in the field of NOx control.

Starch bio-template synthesis of W-doped CeO2 catalyst for selective catalytic reduction of NOx with NH3: influence of ignition temperature

A novel tungsten-doped CeO₂ catalyst was fabricated via the sweet potato starch bio-template spread self-combustion (SSC) method to secure a high NH₃-SCR activity. The study focuses on the influence of ignition temperature on the physical structure and redox properties of the synthesized catalyst and the catalytic performance of NO_x reduction with NH₃. These were quantitatively examined by conducting TG-DSC measurements of the starch gel, XRD analysis for the crystallites, SEM and TEM assessments for the morphology of the catalyst, XPS and H₂-TPR measurements for the distribution of cerium and tungsten, and NH₃-TPD assessments for the acidity of the catalyst. It is found that the ignition temperature shows an important role in the interaction of cerium and tungsten species, and the optimal ignition temperature is 500 °C. The increase of ignition temperature from 150 °C is beneficial to the interactions of species in the catalyst, depresses the formation of WO₃, and refines the cubic CeO₂ crystallite. The sample ignited at 500 °C shows the biggest BET surface area, the highest surface concentration of Ce species and molar ratio of Ce³⁺/(Ce³⁺+Ce⁴⁺), and the most abundant surface Brønsted acid sites, which are the possible reasons for the superiority of the NH₃-SCR activity. With a high GHSV of 200,000 mL (g h)^-1 and the optimal ignition temperature, Ce₄W₂O_z-500 can achieve a steadily high NO_x reduction of 80% or more at a lowered reduction temperature in the range of 250~500 °C.

Effect of CaCO3 on catalytic activity of Fe–Ce/Ti catalysts for NH3-SCR reaction

In the present work, fresh and Ca poisoned Fe–Ce/Ti catalysts were prepared and used for the NH₃-SCR reaction to investigate the effect of Ca doping on the catalytic activity of catalysts. And these catalysts were characterized by BET, XRD, Raman, UV-vis DRS, XPS, H₂-TPR, and NH₃-TPD techniques. The obtained results demonstrate that Ca doping could lead to an obvious decrease in the catalytic activity of catalysts. The reasons for this may be due to the smaller specific surface area and pore volume, the decreased ratio of Fe³⁺/Fe²⁺ and Ce³⁺/Ce⁴⁺, as well as the reduced redox ability and surface acidity.

In the present work, fresh and Ca poisoned Fe–Ce/Ti catalysts were prepared and used for the NH₃-SCR reaction to investigate the effect of Ca doping on the catalytic activity of catalysts.

Effect of ceria loading on Zr-pillared clay catalysts for selective catalytic reduction of NO with NH3

The effect of ceria loading on Zr-pillared clay catalysts was investigated and its reaction mechanism was explored.

Deactivation by HCl of CeO2-MoO3/TiO2 catalyst for selective catalytic reduction of NO with NH3

The effect of HCl on a CeO₂–MoO₃/TiO₂ catalyst for the selective catalytic reduction of NO with NH₃ was investigated with BET, XRD, NH₃-TPD, H₂-TPR, XPS and catalytic activity measurements. The results showed that HCl had an inhibiting effect on the activity of the CeO₂–MoO₃/TiO₂ catalyst. The deactivation by HCl of the CeO₂–MoO₃/TiO₂ catalyst could be attributed to pore blockage, weakened interaction among ceria, molybdenum and titania, reduction in surface acidity and degradation of redox ability. The Ce³⁺/Ce⁴⁺ redox cycle was damaged because unreactive Ce³⁺ in the form of CeCl₃ lost the ability to be converted to active Ce⁴⁺ in the SCR reaction. In addition, a decrease in the amount of chemisorbed oxygen and the concentrations of surface Ce and Mo was also responsible for the deactivation by HCl of the CeO₂–MoO₃/TiO₂ catalyst.

The effect of HCl on a CeO₂–MoO₃/TiO₂ catalyst for the selective catalytic reduction of NO with NH₃.