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The effective control of particle size and electron density of metal active sites is challenging yet important for supported nanoparticles, as size effects and promoter effects play vital roles in heterogeneous catalysis on the nanoscale. In this work, we report Pd/C and Sn-Pd/C nanocatalysts for the base-free aerobic oxidation of vanillyl alcohol to vanillin, a challenging reaction not only in the fundamental research of selective oxidation of alcohols but also for the practical transformation of bio-based alcohols to value-added chemicals. We effectively tuned the mean size of Pd nanoparticles from 1.8 to 6.7 nm by varying the temperature used for catalyst preparation and further modified the electron density of the Pd/C catalyst by adding a SnO2 promoter with different loadings. TEM, HAADF-STEM, XPS, CO chemisorption, and in situ DRIFT-IR of CO adsorption characterizations allowed us to get insight into the unique catalytic properties of Pd nanocatalysts. It was conjectured that the base-free aerobic oxidation of vanillyl alcohol to vanillin over the Pd/C catalyst can be a structure-sensitive reaction and the Pd particle size was decisive for the dispersion of Pd, the proportion of catalytically active Pd0 sites, and the intrinsic turnover frequency (iTOF). The 1 wt % Pd/C (1.8 nm) catalyst showed an iTOF value of 268 h–1 and 100% yield to vanillin at 120 °C, 5 bar of O2, and 20 mg of the catalyst within 9 h. We further demonstrated that Sn4+ ions in SnO2 as an electronic promoter can promote Pd/C activity by the formation of highly active, electron-sufficient Pd0 sites which significantly lowered the apparent activation energy of reaction. The 0.1Sn-Pd/C catalyst showed a higher iTOF value of 458 h–1 and a yield of 100% to vanillin at 120 °C, 3 bar of O2 and 15 mg of the catalyst within 6 h. Moreover, we verified a satisfying reusability and an adequate substrate scope over the 0.1Sn-Pd/C catalyst.

Pd-promoted CeNiXOY mixed oxides showed high production of imines through the oxidative coupling of amines with alcohols due to the synergistic effect between Pd0 species and redox properties of CeNiXOY.

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High‐surface‐area mesoporous CeO2 (hsmCeO2) was prepared by a facile organic‐template‐induced homogeneous precipitation process and showed excellent catalytic activity in imine synthesis in the absence of base from primary alcohols and amines in air atmosphere at low temperature. For comparison, ordinary CeO2 and hsmCeO2 after different thermal treatments were also investigated. XRD, N2 physisorption, UV‐Raman, H2 temperature‐programmed reduction, O2 temperature‐programmed desorption, EPR spectroscopy, and X‐ray photoelectron spectroscopy were used to unravel the structural and redox properties. The hsmCeO2 calcined at 400 °C shows the highest specific surface area (158 m2 g−1), the highest fraction of surface coordinatively unsaturated Ce3+ ions (18.2 %), and the highest concentration of reactive oxygen vacancies (2.4×1015 spins g−1). In the model reaction of oxidative coupling of benzyl alcohol and aniline, such an exceptional redox property of the hsmCeO2 catalyst can boost benzylideneaniline formation (2.75 and 5.55 mmol gceria-1  h−1 based on >99 % yield at 60 and 80 °C, respectively) in air with no base additives. It can also work effectively at a temperature of 30 °C and in gram‐scale synthesis. These are among the best results for all benchmark ceria catalysts in the literature. Moreover, the hsmCeO2 catalyst shows a wide scope towards primary alcohols and amines with good to excellent yield of imines. The influence of reaction parameters, the reusability of the catalyst, and the reaction mechanism were investigated.

Mesoporous Mn1ZrxOy solid solution enables efficient imine formation from catalytic oxidative coupling of alcohols and amines at low temperature in an air atmosphere without base additives.

No abstract

Support properties regulation has been a feasible method for the improvement of noble metal catalytic performance. For Pd-based catalysts, TiO2–CeO2 material has been widely used as an important support. However, due to the considerable discrepancy in the solubility product constant between titanium and cerium hydroxides, it is still challenging to synthesize a uniform TiO2–CeO2 solid solution in the catalysts. Herein, an in situ capture strategy was constructed to fabricate a uniform TiO2–CeO2 solid solution as supports for an enhanced Pd-based catalyst. The obtained Pd/TiO2–CeO2-iC catalyst possessed enriched reactive oxygen species and optimized CO adsorption capability, manifesting a superior CO oxidation activity (T 100 = 70 °C) and stability (over 170 h). We believe this work provides a viable strategy for precise characteristic modulation of composite oxide supports during the fabrication of advanced noble metal-based catalysts.