Crystal orientation-dependent activity of tungsten-based catalysts for selective catalytic reduction of NO with NH3

Controlled crystal facet of tungsten trioxide photoanode to improve on-demand hydrogen peroxide production for in-situ tetracycline degradation

Advanced oxidation processes utilizing hydrogen peroxide (H2O2) are widely employed for the treatment of organic pollutions. However, the conventional anthraquinone method for H2O2 synthesis is unsuitable for this application owing to its hazardous and costly nature. Alternative approaches involve a photoelectrochemical method. Herein, tungsten trioxide (WO3) photoanode has been used for the conversion of H2O into H2O2 through oxidation reaction from a PEC system, simultaneously utilizing in-situ generated hydroxyl (OH•) radicals for tetracycline degradation. By manipulating the ratio of crystal facets between (020) and (200) of the WO3 photoanode, a significant improvement in H2O2 production has been achieved by increasing the proportion of (020) facet. The production rate of WO3 photoanode enriched with the (020) facet is approximately 1.9 times higher than that enriched with (200) facet. This enhanced H2O2 production performance can be attributed to the improved formation of OH• radicals and the accelerated desorption of H2O2 on the (020) facet. Simultaneously, the in-situ generated OH• radicals are applied for tetracycline degradation. Under illumination of sunlight stimulator for 180 min, the optimal photoanode achieves a degradation rate of 86.7% for tetracycline. Furthermore, the resulting chemicals have been analyzed, revealing that C8H10O and C7H8O were formed as the primary products. Notably, these products exhibit significantly lower toxicity compared to tetracycline. This study presents a promising approach for the rational design of WO3 based photoanodes for oxidation reaction, including not only H2O2 production but also the efficient degradation of organic pollutants.

Tungsten Oxide Modified V2O5-Sb2O3/TiO2 Monolithic Catalyst: NH3-SCR Activity and Sulfur Resistance

In this study, a V2O5-Sb2O3/TiO2 monolithic catalyst was modified by introducing WO3. The WO3-modified catalyst exhibited enhanced catalytic activity in the measuring temperature range of 175–320 °C. The changes in dispersion of vanadia species were investigated by ultraviolet-visible (UV-Vis) spectroscopy and H2 temperature-programmed reduction (H2-TPR). A durability test was conducted in a wet SO2-containing atmosphere at 220 °C for 25 h. The sulfate deposition was estimated by temperature-programmed decomposition (TPDC) of sulfates, thermo-gravimetric (TG) analysis, and temperature-programmed desorption (TPD) of NH3. Isothermal SO2 oxidation and temperature-programmed surface reaction (TPSR) of NH4HSO4 with NO were performed. Based on these characterizations, effects of WO3 modification on the sulfate tolerance of the catalyst were explored.

Biotemplate Fabrication of Hollow Tubular CexSr1-xTiO3 with Regulable Surface Acidity and Oxygen Mobility for Efficient Destruction of Chlorobenzene: Intrinsic Synergy Effect and Reaction Mechanism

Developing economic and applicable catalysts with elegant chlorine resistance and organic byproduct inhibition capability is of great significance for chlorinated volatile organic compounds (Cl-VOCs) eco-friendly purification. Here, ternary Ce_xSr_1-xTiO₃ catalysts with tunable surface acidity and oxygen species mobility were creatively fabricated using the hollow tubular-structured fruit hair of Platanus (FHP; a widespread greenery waste) as the scaffolding biotemplate. It is shown that the oxygen vacancy (O_v) triggered by the presence of Ce can optimize the synergy between the Lewis acid sites (LAS) and Brønsted acid sites (BAS). High concentration of O_v and BAS promotes the C-Cl cleavage of chlorobenzene (CB) and accelerates the desorption of Cl^• radicals as inorganic chlorine. Simultaneously, the strong electron transfer within Ti-Ce-Sr linkage increases the acidity of LAS, resulting in the superior reducibility of Ce_0.4Sr_0.6TiO₃ and facilitating the deep oxidation of dechlorination intermediates. Additionally, the spatial confinement of the tubular structure remarkably accelerates the CB flow rate and reduces the residence time of byproducts over the prepared catalysts. Owing to these, CB can be efficiently destructed over Ce_0.4Sr_0.6TiO₃ with selectivity of CO₂ and inorganic chlorine dramatically enhanced, respectively, approximately 16 and 21 times at 275 °C compared to those of pure SrTiO₃. The present work provides a feasible and promising strategy for engineering efficient catalysts for heterogeneous thermocatalytic reactions for industrial-scale Cl-CVOC destruction.

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.

Meziane K, Kaddouri A, Nguyen HP, Taoufik M. Well-defined surface tungstenocarbyne complex through the reaction of [W(CtBu)(CH2tBu)3] with CeO2: a highly stable precatalyst for NOx reduction with NH3

A highly-efficient NH₃-SCR single site catalyst W(CtBu)(CH₂tBu)₃/CeO_2–200, was prepared by surface organometallic chemistry approach. This catalyst showed high catalytic activity and stability with a broad operational temperature window.

In situ decorated MOF-derived Mn–Fe oxides on Fe mesh as novel monolithic catalysts for NOx reduction

In situ decorated MOF-derived Mn–Fe oxides on Fe mesh were developed as novel monolithic catalysts for NO_x reduction.