Debao Li

The direct synthesis of ethanol from syngas faces a key challenge: achieving high selectivity at high CO conversion while elucidating the catalytic reaction mechanism. Here, we develop a catalyst comprising highly dispersed Rh–Fe bimetallic nano-islands supported on mixed-phase TiO2, which overcomes the trade-off between catalytic activity and ethanol selectivity, achieving an ethanol selectivity of 62.5% among all carbon-containing products at a CO conversion of 55.8%. Meanwhile, CO2 selectivity is greatly reduced to 8.1%. Mechanistic studies reveal that the breakthrough stems from the enhanced density of interfacial active sites, that the Fe species modulate the local electronic environment to optimize the Rhδ+/Rh0 ratio, and Rhδ+ species in contact with the TiO2 support are stably anchored via the formation of FeOx–Rhδ+–Ov–Ti3+ interfacial sites. The in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS), chemical transient kinetics (CTK), and density functional theory (DFT) characterizations reveal that the surface Rh0 sites facilitate CO dissociation and hydrogenation, whereas the FeOx–Rhδ+–Ov–Ti3+ interfacial sites promote the coupling of CHx with CHxO while suppressing the CO* + O → CO2 pathway. This work provides a route for suppressing CO2 formation and enhancing ethanol production in syngas conversion.

The selective oxidation of n-butane to maleic anhydride (MA) over the vanadium phosphorus oxide (VPO) catalyst stands as a prominent example of industrial selective alkane functionalization. Despite its commercial maturity, the ambiguous relationship between the catalytic performance and vanadium valence states (V_ox) or surface lattice oxygen (O_S-L) persists in generating debate and uncertainty regarding the identity of the active sites in VPO catalysts. Herein, we reconcile this debate by demonstrating that the catalytic efficiency is governed by valence-state-dependent O_S-L rather than by merely the O_S-L content. Using time-resolved H₂-TPR experiments, we successfully distinguished two distinct types of valence-state-dependent O_S-L: V⁵⁺-O_S-L (O_S-L related to the V⁵⁺ phase) and V⁴⁺-O_S-L (O_S-L related to the V⁴⁺ phase). Their specific functions were then elucidated through a combination of in situ reactant-specific H₂-TPR experiments (utilizing n-butane, 1,3-butadiene, or propylene as probes) and ¹⁸O-isotopic labeling studies. The results clearly demonstrate that V⁵⁺-O_S-L is identified as the site for the initial hydrogen abstraction from n-butane, while V⁴⁺-O_S-L facilitates the crucial epoxidation step to form MA. Furthermore, by employing CeO₂ as a modulator, we precisely tune the V⁵⁺-O_S-L/V⁴⁺-O_S-L ratio through the formation of Ce–O–V bonds, as evidenced by the X-ray absorption near edge (XANES) and extended X-ray absorption fine structure (EXAFS) analysis. An optimal V⁵⁺-O_S-L/V⁴⁺-O_S-L ratio for MA synthesis is 2.22–2.82; otherwise, it would be more conducive to a nonselective reaction. This work introduces a novel design paradigm for the development of high-performance VPO catalysts, offering a comprehensive framework for the rational design of heterogeneous oxidation catalysts via precise control of valence-specific oxygen chemistry.

In this study, two types of catalysts were prepared by the combination of gemini quaternary ammonium salt with two distinct species of phosphotungstic acid. Catalysts prepared by the Wells–Dawson type of phosphotungstic acid and Keggin-type phosphotungstic acid both exhibited dual-phase catalytic behavior, demonstrating both heterogeneous and homogeneous catalytic activities. In comparison to the catalyst prepared by the Keggin-type phosphotungstic acid, due to the higher size of Wells–Dawson type of phosphotungstic acid, hydrogen bonding could not effectively affect the catalyst prepared by H₆P₂W₁₈O₆₂. Subsequently, the influential factors on the catalytic reaction were investigated. Through the utilization of techniques such as XPS, FT-IR, Raman spectra and other characterization methods, two distinct structure and reaction mechanisms for these catalysts were elucidated under the influence of hydrogen bonding.

The base-free oxidation of furfural by non-noble metal systems has been challenging. Although MnO₂ emerges as a potential catalyst application in base-free conditions, its catalytic efficiency still needs to be improved. The crystalline form of MnO₂ is an important factor affecting the oxidation ability of furfural. For this reason, four crystalline forms of MnO₂ (α, β, γ, and δ-MnO₂) were selected. Their oxidation performance and surface functional groups were analyzed and compared in detail. Only δ-MnO₂ exhibited excellent activity, achieving 99.04% furfural conversion and 100% Propo._FA (Only furoic acid was detected by HPLC in the product) under base-free conditions, while the furfural conversion of α, β, and γ-MnO₂ was below 10%. Characterization by XPS, IR, O₂-TPD and other means revealed that δ-MnO₂ has the most abundant active oxygen species and surface hydroxyl groups, which are responsible for the best performance of δ-MnO₂. This work achieves the green and efficient oxidation of furfural to furoic acid over non-noble metal catalysts.