Selective C–C Bond Cleavage in Diols and Lignin Models: High-Throughput Screening of Metal Oxide-Anchored Vanadium in Mesoporous Silica

Abstract

The development of selective and robust heterogeneous oxidation catalysts is an enabling technology for conversion of biomass-derived platform chemicals. Vanadium active sites were incorporated into the structure of mesoporous silica via an ultra-fast, one-pot synthesis method based on microwave-assisted heating. In addition, Al/Ti/Zr/Ce anchoring ions were introduced in order to minimize vanadium leaching and better control its dispersion. The supported V-(Al/Ti/Zr/Ce)-MCM-41 composite materials were assessed as catalysts for aerobic C–C bond cleavage of simple models for lignin (1,2-diphenyl-2-methoxyethanol) and sugar-derived polyalcohols (meso-hydrobenzoin). The TiIV ions proved to be the best anchors to prevent V leaching, while AlIII and ZrIV ions were the best to improve selective conversion of the substrates. The active sites in these catalysts are shown to be 2D VOx layers stabilized on the anchors. In a screen of twelve solvents, weakly polar solvents like toluene were found to be most suitable for this reaction, as was environmentally friendly ethyl acetate. The above properties, together with the high selectivity for C–C bond cleavage, advocate for a heterogeneous catalytic pathway, intrinsically different from that reported previously for molecular oxovanadium (V) catalysts.

Metal-Free Phosphated Mesoporous SiO2 as Catalyst for the Low-Temperature Conversion of SO2 to H2S in Hydrogen

“…For uf-P@m-SiO 2 , the BET surface area is 533 m 2 /g, the pore volume is 0.38 cm 3 /g, and the BJH pore size sharp peaks are centered at 2.5 nm, which is attributed to the mesoporous channels. Compared to the surface area and pore volume of MCM-41 in the literature (~1000 m 2 /g,~1.0 cm 3 /g) [21,22], the pores of uf-P@m-SiO 2 are partially occupied, covered with the residual surfactant, and incorporated of P into the SiO 2 structure, the latter being an active nonporous phase.…”

“…Microwave synthesis of m-SiO2 [21,22]. A 16 g amount of NaOH was dissolved in 400 mL H2O, then 94 mL Ludox (40 wt.%) was added to the above NaOH solution.…”

“…A 1.0 g amount of CTAB and 35 mL H2O were mixed in a sealed polypropylene bottle, then the above solution was stirred slowly at 60 °C for 1 h to achieve a clear viscous solution. At the [21,22]. A 16 g amount of NaOH was dissolved in 400 mL H 2 O, then 94 mL Ludox (40 wt.%) was added to the above NaOH solution.…”

“…Then, the white solid was dried in an oven at 80 • C overnight to obtain an average of 1.5 g white powder m-SiO 2 . (b) Preparation of m-SiO 2 -cal [21,22]. The above-mentioned m-SiO 2 was calcined in a tube furnace with the following stepwise process: the calcination program was set as 2 • C/min to ramp up from room temperature to 550 • C, and heating at 550 • C for 6 h, then cooled down in air.…”

“…The low-angle XRD patterns of samples in Figure 1 display three characteristic peaks corresponding to the (100), (110), and (200) plane diffractions, respectively, typical of the hexagonal structure (p6mm symmetry) of MCM-41 [21,22]. In addition to the broad peak originating from the amorphous SiO 2 at around 20 • [23], no other obvious peaks were observed between 2θ of 10 • and 70 • (Figure S1), showing the absence of any crystalline phase related to P species.…”