Surface Reconstruction of La2CuO4 during the Electrochemical Reduction of Carbon Dioxide to Ethylene and Its Benefits for Enhanced Performance.

Electrochemical reduction (ECR) of CO2 to C2H4 has a potential key role in realizing the carbon neutral future, which ultimately relies on the availability of an efficient electrocatalyst that can exhibit a high Faradaic efficiency (FE) for C2H4 production and robust, long-term operational stability. Here, for the first time, we report that upon applying reductive potential and electrolyte to the benchmark La2CuO4 catalyst, surface reconstruction occurred, i.e., the appearance of a distinctive phase evolution process over time, which was successfully monitored using ex situ powder XRD and operando Mott-Schottky (M-S) measurements of La2CuO4 samples that were soaked into the electrolyte and subjected to CO2-ECR for different durations. At the end of such a reconstruction process, an outermost layer consisting of lanthanum carbonate, a thin outer layer made of an amorphous Cu+ material formed over the core bulk La2CuO4, as confirmed by various characterization techniques, which resulted in the redistribution of interfacial electrons and subsequent formation of electron-rich and electron-deficient interfaces. This contributed to the enhancement in FE for C2H4, reaching as much as 58.7%. Such surface reconstruction-induced electronic structure tuning gives new explanations for the superior catalytic performance of La2CuO4 perovskite and also provides a new pathway to advance CO2-ECR technology.

A lost piece of the puzzle of the alkane cracking mechanism: a carbanion pathway on a solid base catalyst.

The alkane cracking mechanism has been a subject of intense scrutiny, with carbonium and free radical mechanisms being two well-established pathways which correlate to solid acid catalysis and thermal cracking, respectively. However, despite an understanding of these two mechanisms, certain intricacies remain unexplored, especially when it comes to alternative reaction routes over solid base materials. This gap in the knowledge hinders optimization of the desired product selectivity of alkane cracking processes. In this work, solid superbases were first prepared by impregnation of NaNO3 on MgO. The Na/MgO catalysts were characterized by XRD, BET, XPS and CO2-TPD techniques. To investigate the role of solid base materials, propane cracking was conducted over MgO and Na/MgO. SiO2 was chosen as a representative of thermal cracking. Na/MgO showed better selectivity for light olefins than MgO or SiO2. Ethylene and light olefin selectivity could reach about 65.8% and 91.7%, respectively. Meanwhile, in terms of Na/MgO, the ratio of ethylene selectivity and propylene selectivity is greater than 2, exhibiting the advantage of selectivity for ethylene, which is obviously different from MgO and SiO2. Propane cracking over Na/MgO with different loading amounts of NaNO3 was investigated further. The conversion rates of the samples presented a "volcano curve" with increasing Na content. Furthermore, DFT calculation showed that the base-catalyzed process of the propane cracking reaction follows a carbanion mechanism. The better product distribution and stronger surface base sites can be ascribed to charge transfer arising from the loading of NaNO3.

From bench to industry, the application of all-inorganic solid base materials in traditional heterogeneous catalysis: a mini review.

Acids and bases generally occur in pairs as concepts, and a large number of catalytic reactions can be considered as interactions between acids and bases. Many chemical reactions are a combination of acid-catalyzed processes and base-catalyzed processes, and thus it is particularly important to study and explain the mechanisms of acid-base synergy or acid-base interactions. However, compared to the in-depth research on acid catalysts, there is a lack of research on solid bases. In addition to the application of basic materials to non-petroleum processes, recent studies have also applied basic materials to the catalytic cracking reaction process of heavy oils, providing new ideas for the processing of heavy oils. The formation of carbanions with the contribution of basicity is a critical stage in many fine chemical reactions, as well as in the hydrocarbon cracking reactions promoted by a base. Thus, herein, we summarize the research progress on the main types of all-inorganic solid base catalysts, including the types of catalysts used in non-petroleum processes and petroleum processes, their preparation, the properties of their basic sites, and their structure-performance correlation in the reactions. Also, we provide an outlook on the future research directions of all-inorganic solid base materials.

Effect of Polymer Removal on the Morphology and Phase of the Nanoparticles in All-Inorganic Heterostructures Synthesized via Two-Step Polymer Infiltration.

Polymer templates play an essential role in the robust infiltration-based synthesis of functional multicomponent heterostructures with controlled structure, porosity, and composition. Such heterostructures are be used as hybrid organic-inorganic composites or as all-inorganic systems once the polymer templates are removed. Using iron oxide/alumina heterostructures formed by two-step infiltration of polystyrene-block-polyvinyl pyridine block copolymer with iron and aluminum precursors from the solution and vapor-phases, respectively, we show that the phase and morphology of iron oxide nanoparticles dramatically depend on the approach used to remove the polymer. We demonstrate that thermal and plasma oxidative treatments result in iron oxide nanoparticles with either solid or hollow morphologies, respectively, that lead to different magnetic properties of the resulting materials. Our study extends the boundaries of structure manipulations in multicomponent heterostructures synthesized using polymer infiltration synthesis, and hence their properties.

Revealing the Effects of the Non-solvent on the Ligand Shell of Nanoparticles and Their Crystallization.

When nanoparticles (NPs) are assembled from solution, a common assembly method of choice is either solution destabilization or solvent evaporation technique. The destabilization of the NP solution by non-solvents results in the formation of faceted supercrystals (SCs) while periodic film-like assemblies are typically formed by solvent evaporation. Here, we reveal the effect of non-solvents in washing, dispersing, and crystallizing NPs. Small angle neutron scattering (SANS) is employed for monitoring the ligand shell of NPs in solutions upon introduction of various non-solvents. The SC crystallization process is traced in situ with small-angle X-ray scattering (SAXS), and the structures of the resulting single-crystalline SCs are examined in detail by mapping the reciprocal space using SAXS and wide-angle X-ray scattering. Our study suggests that the relative miscibility of the non-solvent with solvents and ligands determines the solvation and thickness of the ligand shell and thereby the resulting structure of SCs. In the early stage of crystallization, truncated octahedral PbS NPs form SCs with face-centered cubic (fcc) symmetry. In the later stage, the fcc symmetry is preserved in the SC formed by larger (5.60 nm) NPs, but the SC assembled from smaller (4.14 nm) NPs undergoes a phase transition into body-centered cubic (bcc) lattice via Bain transformation, becoming a polycrystalline SC containing three structurally correlated bcc domains and one untransformed fcc domain. Our study provides the detailed understanding of the non-solvent effect that impacts beyond the formation of SCs, enabling the judicious selection of solvent/non-solvent mixtures for NP purification.

XANES/EPR Evidence of the Oxidation of Nickel(II) Quinolinylpropioamide and Its Application in Csp3 -H Functionalization.

An in situ generated oxidation species of nickel quinolinylpropioamide intermediate was produced. Characterization by X-ray absorption near edge structure (XANES) and EPR provides complementary insights into this oxidized nickel species. With aliphatic amides and isocyanides as substrates, a nickel-catalyzed facile synthesis of structurally diverse five-membered lactams could be achieved.

Pd/Cu-catalyzed dual C-H bond carbonylation towards the synthesis of fluorazones.

Pd/Cu catalyzed oxidative dual C-H bond activation/carbonylation still remains a great challenge due to the generation of by-products via C-C bond formation. Herein we developed a straightforward Pd/Cu-catalyzed oxidative dual C-H bond carbonylation process to access biologically and pharmaceutically important fluorazones from easily available N-aryl pyrroles and CO. A wide range of functional groups were well tolerated in this transformation, and O2 could be utilized as the only terminal oxidant to promote the oxidative carbonylation process.

(E)-α,ß-unsaturated amides from tertiary amines, olefins and CO via Pd/Cu-catalyzed aerobic oxidative N-dealkylation.

A novel Pd/Cu-catalyzed chemoselective aerobic oxidative N-dealkylation/carbonylation reaction has been developed. Tertiary amines are utilized as a "reservoir" of "active" secondary amines in this transformation, which inhibits the formation of undesired by-products and the deactivation of the catalysts. This protocol allows for an efficient and straightforward construction of synthetically useful and bioactive (E)-α,ß-unsaturated amide derivatives from easily available tertiary amines, olefins and CO.

Palladium/copper-catalyzed oxidative C-H alkenylation/N-dealkylative carbonylation of tertiary anilines.

C-H/C-N activation: The first palladium/copper-catalyzed aerobic oxidative C-H alkenylation/N-dealkylative carbonylation of tertiary anilines has been developed. Various functional groups were tolerated and acrylic ester could also be suitable substrates. This transformation provided efficient and straightforward synthesis of biologically active 3-methyleneindolin-2-one derivatives from cheap and simple substrates.