Effective Control of Particle Size and Electron Density of Pd/C and Sn-Pd/C Nanocatalysts for Vanillin Production via Base-Free Oxidation

Abstract

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.

Hydrogenative coupling of nitriles with diamines to benzimidazoles using lignin-derived Rh2P catalyst

“…The TEM images of Pd/LC 400 indicate a significantly increased average size to 18.3 nm for Pd nanoparticle on the support ( Figures 2 G and 2H). The observed lattice fringe spacing was detected as 0.224 nm, belonging to the (111) plane of Pd ( Sun et al., 2020 ) ( Figure 2 I). Finally, for Ru/LC 400 sample, TEM images show an average nanoparticle size of 3.3 nm ( Figures 2 J and 2K) with the lattice fringe spacing around 0.214 nm, corresponding to the (002) plane of Ru ( Wang et al., 2020 ) ( Figure 2 L).…”

Influence of Calcination on Mesoporous Mn1Zr0.5Oy Solid Solution in Oxidative Coupling Catalysis for Benzylideneaniline Formation

“…Hence, the basic sites (i. e., OH − as Brønsted base and O 2− as Lewis base) on the Mn 1 Zr 0.5 O y catalyst could probably promote the activation of OH group in benzyl alcohol to form the alkoxide intermediate [5a,21] . In addition, the Brønsted acidic sites due to metal −OH + may usually facilitate the formation of C=O group in an aldehyde [22] . The Lewis acidic sites due to Mn cations can bring about the formation of Vö and O latt.…”

“…[5a,21] In addition, the Brønsted acidic sites due to metal À OH + may usually facilitate the formation of C=O group in an aldehyde. [22] The Lewis acidic sites due to Mn cations can bring about the formation of Vö and O latt. species.…”

Hydrogenative Coupling of Nitriles with Diamines to Benzimidazoles Using Lignin-Derived Rh ₂p Catalyst

“…The TEM images of Pd/LC 400 indicate a significantly increased average size to 18.3 nm for Pd nanoparticle on the LC support (Figures 2G and 2H). The observed lattice fringe spacing was detected as 0.224 nm, belonging to the (111) plane of Pd (Sun et al, 2020) (Figure 2I). Finally, for Ru/LC 400 sample, TEM images show an average nanoparticle size of 3.3 nm (Figures 2J and 2K) with the lattice fringe spacing around 0.214 nm, corresponding to the (002) plane of Ru (Wang et al, 2020) (Figure 2L).…”