ZnO modified TiO2 nanotube array supported Pt catalyst for HCHO removal under mild conditions

Efficient degradation of formaldehyde based on DFT-screened metal-doped C3N6 monolayer photocatalysts: performance evaluation and mechanistic insights

Photocatalytic oxidation is an efficient and promising technology for reducing indoor pollution levels of formaldehyde (HCHO). However, developing efficient and low-cost photocatalysts for the removal of HCHO remains challenging due to the time-consuming and expensive nature of traditional "trial and error" and "directed research" approaches. To achieve this goal, first-principles density functional theory (DFT) calculations were conducted to high-throughput screen candidate TM-C3N6 photocatalysts for high-performance degradation of HCHO. The results revealed that Zr-C3N6 and Hf-C3N6 in functionalizing C3N6 with 28 transition metals showed excellent adsorption energy of HCHO, boosting the highly effective capture of HCHO. Meanwhile, an excellent adsorption performance mechanism was further elicited by the electric structure-property relationship. In addition, reaction mechanisms for HCHO degradation and three potential reaction pathways for HCHO degradation were systematically evaluated. Our findings indicated that hydroxyl-assisted dehydrogenation and oxygen-assisted dehydrogenation are the most favorable pathways, with rate-limiting steps involving the formation of ˙OH and ˙O radicals. Overall, this study may provide new insights into a high-throughput screening of novel photocatalysts that are both high-performing and low-cost for the removal of formaldehyde. This, in turn, can accelerate the experimental development process and reduce the associated costs and time consumption.

Electronic Modification by Transitional Metal Dopants to Tune the Oxidation Activity of Pt-CeO2-Based Catalysts

While utilization of transitional metals as a promoter has been extensively studied to enhance the activity of Pt-based catalysts for the oxidation of formaldehyde (HCHO), there is still a lack of well elucidated property-function relationship for the rational selection of a promoter in catalyst design. Herein, we modified a Pt/CeO₂ catalyst with two transitional metal dopants (i.e., Mn and Cu) that showed negligible influence on the physical structure of the Pt-CeO₂ matrix but distinct effects on the activity of the catalyst. Complementary characterizations combined with density functional theory modeling revealed that the transitional metal dopants significantly modified the electronic structure of the catalyst and shifted the d-band of Pt to higher energy with different extents, which may tune the bonding strength of HCHO/intermediates with the Pt-CeO₂ interface domain. The catalyst with moderate bonding strength (i.e., Pt-Mn/CeO₂) displayed the highest reactivity under the ambient condition, while Pt-Cu/CeO₂ with the highest bonding strength showed a dramatically decreased activity. No correlation was observed between the abundancy of the active oxygen and catalytic activity, likely due to the oxygen supply having a much higher rate than the rate-determining step. This work contributes to the elucidation about the property-function relationship of a transitional metal dopant in Pt-based catalysts for the oxidation of HCHO.

Hydrothermal oxygen uncoupling of high-concentration biogas slurry over Cu-α-Fe2O3·α-MoO3 catalyst

A hydrothermal oxygen uncoupling (HTOU) method which combines aqueous phase reforming (APR) and oxygen uncoupling was proposed to treat biogas slurry (BS). Based on Le Chatelier's principle, this novel approach was constructed and realized by Cu-α-Fe₂O₃·α-MoO₃ catalyst with van der Waals heterojunction-redox property. Additionally, the catalyst was synthesized by integrating a simple one-pot sol-gel method and thermal hydrogenating. Results indicated that the optimal removal efficiencies of non-purgeable organic carbon (NPOC) (76.29%), total nitrogen (TN) (45.56%), and ammonia nitrogen (AN) (29.03%) were achieved on the Cu-α-Fe₂O₃·α-MoO₃ catalyst at 225.00 °C for 30.00 min, respectively. The significant performance of Cu-α-Fe₂O₃·α-MoO₃ could be attributed to three aspects. (1) The α-MoO₃ nanosheets with van der Waals heterostructures obtained at the calcination temperature of 600.00 °C, which can provide the superior performance of APR for hydrogen generation. (2) The adsorbed oxygen species were eliminated by thermal hydrogenating which had a surface passivation effect. (3) The effect of oxygen uncoupling in the lattice oxygen and gaseous oxygen release reaction was beneficial to the degradation of organic matter. Moreover, the reuse of catalysts studies further revealed that the deactivation of catalysts originated from carbon deposition of aromatic polymers and heavy metals oxides pollution. Overall, these findings disclosed that the HTOU could be a promising alternative to the treatment of high-concentration organic wastewater.

Active Complexes on Engineered Crystal Facets of MnOx-CeO2 and Scale-Up Demonstration on an Air Cleaner for Indoor Formaldehyde Removal

Crystal facet-dominated surfaces determine the formation of surface-active complexes, and engineering specific facets is desirable for improving the catalytic activity of routine transition-metal oxides that often deactivate at low temperatures. Herein, MnO_x-CeO₂ was synthetically administered to tailor the exposure of three major facets, and their distinct surface-active complexes concerning the formation and quantitative effects of oxygen vacancies, catalytically active zones, and active-site behaviors were unraveled. Compared with two other low-index facets {110} and {001}, MnO_x-CeO₂ with exposed {111} facet showed higher activity for formaldehyde oxidation and CO₂ selectivity. However, the {110} facet did not increase activity despite generating additional oxygen vacancies. Oxygen vacancies were highly stable on the {111} facet, and its bulk lattice oxygen at high migration rates could replenish the consumption of surface lattice oxygen, which was associated with activity and stability. High catalytically active regions were exposed at the {111}-dominated surfaces, wherein the predominated Lewis acid-base properties facilitated oxygen mobility and activation. The mineralization pathways of formaldehyde were examined by a combination of in situ X-ray photoemission spectroscopy and diffuse reflectance infrared Fourier transform spectrometry. The MnO_x-CeO₂-111 catalysts were subsequently scaled up to work as filter substrates in a household air cleaner. In in-field pilot tests, 8 h of exposure to an average concentration of formaldehyde after start-up of the air cleaner attained the Excellent Class of Indoor Air Quality Objectives in Hong Kong.

New insight into the enhanced catalytic performance of ZnPt/HZSM-5 catalysts for direct dehydrogenation of propane to propylene

Framework Zn species and small-sized PtZn particles in ZnPt/HZSM-5 catalyst function cooperatively in PDH, showing excellent performance at 525 °C.

Steam Reforming of Methanol over Nanostructured Pt/TiO2 and Pt/CeO2 Catalysts for Fuel Cell Applications

A research and technological challenge for fuel processors integrated with High Temperature Polymer Electrolyte Membrane Fuel Cells (HT-PEMFCs), also known as Internal Reforming Methanol Fuel Cells (IRMFCs), operating at 200–220 °C, is the development of highly efficient catalysts, which will be able to selectively (low CO and other by-products formation) produce the required quantity of hydrogen at these temperatures. In this work, various amounts of platinum were dispersed via deposition-precipitation (DP) and impregnation (I) methods onto the surface of hydrothermally prepared ceria nanorods (CNRs) and titania nanotubes (TNTs). These nanostructured catalysts were evaluated in steam reforming of methanol process targeting the operation level of IRMFCs. The (DP) method resulted in highly (atomically) dispersed platinum-based catalysts, as confirmed with Scanning Transmission Electron Microscopy (STEM) analysis, with a mean particle size of less than 1 nm in the case of 0.35 wt.% Pt/CNRs catalyst. Ultra-fine dispersion of platinum species correlated with the presence of oxygen vacancies, together with the enrichment of CNRs surface with active metallic phase resulted in a highly active catalyst achieving at 220 °C a hydrogen production rate of 5500 cm3 min−1 per g of loaded platinum.

Synthesis of Nano-Zinc Oxide Loaded on Mesoporous Silica by Coordination Effect and Its Photocatalytic Degradation Property of Methyl Orange

Salicylaldimine-modified mesoporous silica (Sal-MCM-3 and Sal-MCM-9) was prepared through a co-condensation method with different amounts of added salicylaldimine. With the coordination from the salicylaldimine, zinc ions were impregnated on Sal-MCM-3 and Sal-MCM-9. Then, Zn-Sal-MCM-3 and Zn-Sal-MCM-9 were calcined to obtain nano-zinc oxide loaded on mesoporous silica (ZnO-MCM-3 and ZnO-MCM-9). The material structures were systematically studied by Fourier transform infrared spectroscopy (FTIR), N₂ adsorption/desorption measurements, X-ray powder diffraction (XRD), zeta potential, scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), ultraviolet diffused reflectance spectrum (UV-vis DRS), and thermogravimetry (TGA). Methyl orange (MO) was used to investigate the photocatalysis behavior of ZnO-MCM-3 and ZnO-MCM-9. The results confirmed that nano ZnO was loaded in the channels as well as the outside surface of mesoporous silica (MCM-41). The modification of salicylaldimine helped MCM-41 to load more nano ZnO on MCM-41. When the modification amount of salicylaldimine was one-ninth and one-third of the mass of the silicon source, respectively, the load of nano ZnO on ZnO-MCM-9 and ZnO-MCM-3 had atomic concentrations of 1.27 and 2.03, respectively. ZnO loaded on ZnO-MCM-9 had a wurtzite structure, while ZnO loaded on ZnO-MCM-3 was not in the same crystalline group. The blocking effect caused by nano ZnO in the channels reduced the orderliness of MCM-41. The photodegradation of MO can be divided in two processes, which are mainly controlled by the surface areas of ZnO-MCM and the loading amount of nano ZnO, respectively. The pseudo-first-order model was more suitable for the photodegradation process.