Facet-Dependent selectivity of CeO2 nanoparticles in 2-Propanol conversion

Synthesis of Double Trivalent Perovskite Quantum Dots Cs3BiSbX9 (X = Cl, Br, I) for Efficient CO2 Photoreduction Performance

Non-toxic Bi halides have great potential in the field of CO2 photoreduction, but strong charge localization limits their charge separation and transfer. In this study, a series of Cs3BiSbX9 (X = Cl, Br, I) perovskite quantum dots (PQDs) are synthesized by antisolvent recrystallization at room temperature, in which Cs3BiSbBr9 PQDs has high selectivity (94.51%) and yield (15.32 µmol g-1 h-1) of CO2 to CO. In situ DRIFTS and theoretical calculations suggest that the surface charge can be tailored by halogen modulation, allowing for the customization of intermediate species. The Bi─Br─Sb symmetric charge distribution induced by the halogen Br promotes the formation of b─HCOO and reduces the reaction energy barrier of the rate-limiting step, while the weak electronegativity of Cl and the high electronegativity of I leads to m─HCOO and ─COOH production, which are detrimental to CO generation. This work provides new insights into the design of halide alloy perovskites for CO2 photoreduction.

N2 as an Efficient IR Probe Molecule for the Investigation of Ceria-Containing Materials

Ceria and ceria-based catalysts are very important in redox and acid-base catalysis. Nanoceria have also been found to be important in biomedical applications. To design efficient materials, it is necessary to thoroughly understand the surface chemistry of ceria, and one of the techniques that provides such information about the surface is the vibrational spectroscopy of probe molecules. Although the most commonly used probe is CO, it has some disadvantages when applied to ceria and ceria-based catalysts. CO can easily reduce the material, forming carbonate-like species, and can be disproportionate, thus modifying the surface. Here, we offer a pioneering study of the adsorption of 15N2 at 100 K, demonstrating that dinitrogen can be more advantageous than CO when studying ceria-based materials. As an inert gas, N2 is not able to oxidize or reduce cerium cations and does not form any surface anionic species able to modify the surface. It is infrared and transparent, and thus there is no need to subtract the gas phase spectrum, something that often increases the noise level. Being a weaker base than CO, N2 has a negligible induction effect. By using stoichiometric nano-shaped ceria samples, we concluded that 15N2 can distinguish between surface Ce4+ sites on different, low index planes; with cations on the {110} facets and on some of the edges, Ce4+-15N2 species with IR bands at 2258-2257 cm-1 are formed. Bridging species, where one of the N atoms from the molecule interacts with two Ce4+ cations, are formed on the {100} facets (2253-2252 cm-1), while the interaction with the {111} facets is very weak and does not lead to the formation of measurable amounts of complexes. All species are formed by electrostatic interaction and disappear during evacuation at 100 K. In addition, N2 provides more accurate information than CO on the acidity of the different OH groups because it does not change the binding mode of the hydroxyls.

Photocatalytic Co-Reduction of N2 and CO2 with CeO2 Catalyst for Urea Synthesis

The effective conversion of carbon dioxide (CO2 ) and nitrogen (N2 ) into urea by photocatalytic reaction under mild conditions is considered to be a more environmentally friendly and promising alternative strategies. However, the weak adsorption and activation ability of inert gas on photocatalysts has become the main challenge that hinder the advancement of this technique. Herein, we have successfully established mesoporous CeO2-x nanorods with adjustable oxygen vacancy concentration by heat treatment in Ar/H2 (90 % : 10 %) atmosphere, enhancing the targeted adsorption and activation of N2 and CO2 by introducing oxygen vacancies. Particularly, CeO2 -500 (CeO2 nanorods heated treatment at 500 °C) revealed high photocatalytic activity toward the C-N coupling reaction for urea synthesis with a remarkable urea yield rate of 15.5 μg/h. Besides, both aberration corrected transmission electron microscopy (AC-TEM) and Fourier transform infrared (FT-IR) spectroscopy were used to research the atomic surface structure of CeO2 -500 at high resolution and to monitor the key intermediate precursors generated. The reaction mechanism of photocatalytic C-N coupling was studied in detail by combining Density Functional Theory (DFT) with specific experiments. We hope this work provides important inspiration and guiding significance towards highly efficient photocatalytic synthesis of urea.

A Lewis acid-base paired InBO3 catalyst: synthesis and high selectivity for isopropanol dehydrogenation

Whilst metal borates are well known as optical materials, their potential in solid catalysis has been less investigated. The calcite structured InBO₃ was selected as the target borate and was prepared using a solvothermal method. High-resolution transmission electron microscopy and powder X-ray diffraction prove that the material has a nanoparticle morphology with an average size ∼50 nm and high crystallinity. Intrinsic surface oxygen vacancies, which are beneficial to catalysis, were detected using X-ray photoelectron spectroscopy. Lewis acidity and basicity were both observed using NH₃-/CO₂-temperature-programmed desorption experiments, and the total acid and base amounts were found to be 46.6 and 123.8 μmol g^-1, respectively. Catalytic dehydration and dehydrogenation reactions for isopropanol at elevated temperatures were conducted in a fixed bed reactor to evaluate the catalytic performance of InBO₃. InBO₃ exhibits a high conversion rate (>90.5%) and, most importantly, a high dehydrogenation selectivity (acetone selectivity >92.5%), whilst the optimal acetone yield achieved was 121.3 mmol h^-1 g^-1_cat at 350 °C. This study on InBO₃ strongly suggests that metal borates have promising applications in heterogeneous catalysis.

Expediting Toluene Combustion by Harmonizing the Ce-O Strength over Co-Doped CeZr Oxide Catalysts

Low-temperature catalytic degradation of volatile organic compounds (VOCs) by enhancing the activity of non-precious metal catalysts has always been the focus of attention. The mineralization of aromatic VOCs requires the participation of a large number of oxygen atoms, so the activation of oxygen species is crucial in the degradation reaction. Herein, we originally adjust the Ce-O bond strength in CeZr oxide catalysts by cobalt doping to promote the activation of oxygen species, thus improving the toluene degradation performance while maintaining high stability. Subsequent characterizations and theoretical calculations demonstrate that the weakening of the Ce-O bond strength increases the oxygen vacancy content, promotes the activation of oxygen species, and enhances the redox ability of the catalysts. This strategy also promotes the activation of toluene and accelerates the depletion of intermediate species. This study will contribute a strategy to enhance the activation ability of oxygen species in non-noble metal oxide catalysts, thereby enhancing the degradation performance of VOCs.

Assessment of Lewis-Acidic Surface Sites Using Tetrahydrofuran as a Suitable and Smart Probe Molecule

Measuring the Lewis-acidic surface sites in catalysis is problematic when the material's surface area is very low (SBET ≤1 m2  ⋅ g-1 ). For the first time, a quantitative assessment of total acidic surface sites of very small surface area catalysts (MoO3 as pure and mixed with 5-30 % CdO (wt/wt), as well as CdO for comparison) was performed using a smart new probe molecule, tetrahydrofuran (THF). The results were nearly identical compared to using another commonly used probe molecule, pyridine. This audition is based on the limited values of the surface area of these samples that likely require a relatively moderate basic molecule as THF with pKb =16.08, rather than strong basic molecules such as NH3 (pKb =4.75) or pyridine (pKb =8.77). We propose mechanisms for the interaction of vapour phase molecules of THF with the Lewis-cationic Mo and Cd atoms of these catalysts. Besides, dehydration of isopropyl alcohol was used as a probe reaction to investigate the catalytic activity of these catalysts to further support our findings in the case of THF in a temperature range of 175-300 °C. A good agreement between the obtained data of sample MoO3 -10 % CdO, which is characterised by the highest surface area value, the population of Lewis-acidic sites and % selectivity of propylene at all the applied reaction temperatures was found.