Abstract
The catalytic performances of bifunctional vanadium oxide supported on Hβ zeolite with redox and acid properties were investigated for dimethyl ether (DME) direct oxidation to polyoxymethylene dimethyl ethers (DMMx) (x=1-2). The best catalytic performance was obtained over 15%V2O5/Hβ. The catalysts were characterized by XRD, BET, NH3-TPD, H2-TPR, XPS and FT-IR in order to provide the further insight in the relationship of structure and activity. When the loading content of vanadium oxide was 15%, the presence of oxide species was dominantly the polymeric vanadia. The addition of vanadium oxide to the H-beta zeolite not only provided redox sites, but also changed the acid strength and distribution of H-beta zeolite as confirmed by NH3-TPD measurement, and the positive correlation was found between the DMMx selectivity and the ratio of weak and strong acid sites. The introduction of vanadium oxide with appropriate amount to the H-beta zeolite promoted the balance between the acid sites and redox sites, which was very vital for obtaining high DMMx selectivity.
Highlights
Polyoxymethylene dimethyl ethers (DMMx) have attracted intensive research interest because of their promising properties, such as excellent environmental friendly solvent with low toxicity, low boiling point, good solubility, and the high oxygen content and octane value
We reported the synthesis of DMMx via the direct oxidation of dimethyl ether (DME) over Re/Sm/Mn modified heteropolyacids catalysts [15,16]
The characteristic diffraction peaks of crystalline V2O5 were not detected when the content of vanadium oxide was lower than 15%, suggesting that the VOx species were dispersed highly on the zeolite
Summary
Polyoxymethylene dimethyl ethers (DMMx) have attracted intensive research interest because of their promising properties, such as excellent environmental friendly solvent with low toxicity, low boiling point, good solubility, and the high oxygen content and octane value. DMMx can effectively improve the engine combustion performance of diesel oil to be beneficial to reduce the CH, CO content in the exhaust emissions, it is considered extremely as the promising green diesel additive in the application [1,2]. The dehydration-condensation of methanol with formaldehyde over the acid catalysts was the main method to synthesize DMMx. Compared with the aldolization reaction, the researchers proposed the one-step oxidation of methanol to DMM, which was considered to be more environmental and economical advantages. The V2O5/TiO2 catalysts have been further studied because of the outstanding catalytic performance in direct oxidation of methanol to DMM [7,8,9]
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