Degradation of Formaldehyde over MnO2/CeO2 Hollow Spheres: Elucidating the Influence of Carbon Sphere Self-Sacrificing Templates

Direct Catalytic Oxidation of Low-Concentration Methane to Methanol in One Step on Ni-Promoted BiOCl Catalysts

The direct oxidation of low-concentration methane (CH₄) to methanol (CH₃OH) is often regarded as the "holy grail". However, it still is very difficult and challenging to oxidize methane to methanol in one step. In this work, we present a new approach to directly oxidize CH₄ to generate CH₃OH in one step by doping non-noble metal Ni sites on bismuth oxychloride (BiOCl) equipped with high oxygen vacancies. Thereinto, the conversion rate of CH₃OH can reach 39.07 μmol/(g_cat·h) under 420 °C and flow conditions on the basis of O₂ and H₂O. The crystal morphology structure, physicochemical properties, metal dispersion, and surface adsorption capacity of Ni-BiOCl were explored, and the positive effect on the oxygen vacancy of the catalyst was proved, thus improving the catalytic performance. Furthermore, in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) was also performed to study the surface adsorption and reaction process of methane to methanol in one step. Results demonstrate that the key to keep good activity lies in the oxygen vacancies of unsaturated Bi atoms, which can adsorb and active CH₄ and to produce methyl groups and adsorbing hydroxyl groups in methane oxidation process. This study broadens the application of oxygen-deficient catalysts in the catalytic conversion of CH₄ to CH₃OH in one step, which provides a new perspective on the role of oxygen vacancies in improving the catalytic performance of methane oxidation.

Scalable Preparation of Sub-Millimeter Double-Shelled Al2O3 Hollow Spheres and Their Rapid Separation from Wastewater after Adsorption of Congo Red

Porous double-shelled ceramic hollow spheres (PDSs) have attracted extensive attention due to their high specific surface areas and multifunctional designs. When used in wastewater treatment, millimeter or sub-millimeter spheres can be quickly separated from water by commercial sieves. However, the simple, scalable, and low-cost preparation of sub-millimeter PDSs in the solid phase remains a challenge. Herein, porous PDSs were facilely fabricated via a spheronization process utilizing pseudoboehmite powders and wet gelatin spheres as templates, which broke through the difficulty of preparing PDSs by one-step solid-state synthesis. Treating pseudoboehmite powder with nitric acid can improve the compressive strength of the PDSs. By controlling the rolling time and gelatin concentration of gelatin microspheres, the integrity, shell thickness, and double-shelled spacing of the gelatin microspheres were tuned. When the rolling time was 8-12 min, and the gelatin concentration in gelatin spheres was 250 g/L, and PDSs with a complete double-shelled structure, good mechanical property, and high specific surface area (327.5-509.6 m²/g) were obtained at 600 °C. The adsorption capacities of the PDSs for 100 mg/L Congo red solution (70.7 mg/g) were larger than those of single-shelled hollow spheres (49 mg/g), and larger diameters (608-862 μm) of the PDSs allow them to be rapidly separated from solution by a commercial sieve. This paper provides a facile and scalable method for the preparation of sub-millimeter PDSs and demonstrates their excellent adsorption capacity for Congo red solution.

Template and interfacial reaction engaged synthesis of CeMnO x hollow nanospheres and their performance for toluene oxidation

A series of well-dispersed CeMnO x hollow nanospheres with uniform diameter and thickness were synthesized by a novel approach combining the template method and interfacial reaction. A SiO2 template was used as a hard template for preparation of SiO2@CeO2 nanospheres by solvothermal reaction. SiO2@CeMnO x could be formed after KMnO4 was reacted with SiO2@CeO2 by interfacial reaction between MnO4 - and Ce3+. Among all the prepared catalysts, CeMnO x -3 with a moderate content of Mn (15 wt%) exhibited the lowest temperature for complete combustion of toluene (280 °C). Moreover, it showed high stability for 36 h with toluene conversion above 97.7% and good water tolerance with 5 vol% H2O. With characterization, we found that the reaction between Ce and Mn in the Ce-Mn binary oxides gave rise to increased Ce3+ and oxygen vacancies, which led to the formation of enhanced reducibility and more surface-absorbed oxygens (O2 2-, O2- and O-), and improved the catalytic performance further.