Oxidation of cyclopentene catalyzed by tungsten-substituted molybdophosphoric acids

Sustainable production of organic acids from chitin biomass catalyzed by Keggin-type heteropolyacid under hydrothermal condition

The "shell biorefinery," which valorizes the shell waste chitin into fine chemicals, has developed rapidly in recent years. Herein, we present a novel base-free heteropolyacid-catalyzed oxidation method for the transformation of chitin biomass into organic acid. After a series of optimization experiments, a 5.93 % yield of formic acid and 25.09 % yield of acetic acid were achieved in the presence of 0.5 equivalent of Mo-V-P heteropolyacids (H4PMo11VO40·2H2O) and air at 180 °C under hydrothermal conditions for 4 h. Meanwhile, we have demonstrated that the Keggin-type heteropolyacid catalysts are capable of efficiently converting microcrystalline chitin into organic acids. The synthesized heteropolyacids are well characterized with FT-IR, XRD, ICP-AES, and TGA. The possible reaction pathway was speculated accordingly. This method offers several advantages, including readily available raw materials, simple operation, and relatively higher yield.

Hydrothermal Modification of TS-1 Zeolites with Organic Amines and Salts to Construct Highly Selective Catalysts for Cyclopentene Epoxidation

Developing efficient heterogeneous catalysts for cyclic olefins epoxidation is highly attractive for meeting the growing need for various cyclic epoxides. Herein, hierarchical TS-1 zeolite with relatively abundant mesopores and less amount of surface hydroxyl groups was obtained by hydrothermal modification of an as-synthesized TS-1 zeolite with a mixed solution of ammonia, tetrapropylammonium bromide (TPABr) and KCl. The post-modified TS-1 zeolite exhibited much higher catalytic activity (52% conversion) and epoxide selectivity (98%) for the epoxidation of cyclopentene than the conventional TS-1 zeolites. The excellent catalytic activity of the hierarchical TS-1 could be mainly assigned to the enhancement of the mass transport ability and the accessibility of the active Ti species, while the improvement of epoxidation selectivity may be mainly related to the introduction of a certain amount of K+ that can effectively modulate the coordination environment of Ti species as well as the polarity of the zeolite. This work demonstrated that a highly active and selective catalyst for the H2O2-mediated cyclopentene epoxidation could be obtained by concurrently generating mesopore and extinguishing the unfavorable defective hydroxyl groups through the simple hydrothermal treatment of the conventional TS-1 zeolite with a mixed base/salt solution.

Effect of Cesium and Phosphate Addition to Mo/V/W Mixed Oxide Catalysts for the Gas Phase Oxidation of Methacrolein to Methacrylic Acid

The present study investigates modified Mo/V/W mixed oxides as a possible alternative for state of the art heteropoly acid catalysts (HPA) in the partial oxidation of methacrolein (MAC) to methacrylic acid (MAA). Even though HPAs show an excellent activity and MAA selectivity, their long-term stability is unsatisfying, rendering the catalyst inoperable after runtimes of roughly 6 months. Mo/V/W mixed oxides consisting of M1 and a hexagonal (Mo,V,W)Ox-phase (h-phase) in varying proportions were modified by impregnation with aqueous solutions containing cesium and phosphate ions. All samples were characterized with respect to specific surface area, crystallinity, elemental and phase composition. The catalytic performance in the oxidation of MAC to MAA was investigated using a continuously operated reaction unit with tubular fixed bed reactor. Impregnation with cesium and phosphate ions and subsequent heating triggers the transformation of the mixed oxide into a Keggin-type HPA, whereby the h-phase is more reactive than M1. The transformation into HPA is accompanied by a change in the catalytic properties, i.e., the selectivity to MAA is considerably improved. Compared to HPA synthesized directly, however, the HPA samples obtained by transformation of mixed oxides exhibit no advantages, be it with respect to activity, MAA selectivity or stability.