Abstract
Due to its excellent conductivity, good thermal stability and large specific surface area, carbon nano-tubes (CNTs) were selected as support to prepare a Re-based catalyst for dimethyl ether (DME) direct oxidation to polyoxymethylene dimethyl ethers (DMMx). The catalyst performance was tested in a continuous flow type fixed-bed reactor. H3PW12O40 (PW12) was used to modify Re/CNTs to improve its activity and selectivity. The effects of PW12 content, reaction temperature, gas hourly space velocity (GHSV) and reaction time on DME oxidation to DMMx were investigated. The results showed that modification of CNT-supported Re with 30% PW12 significantly increased the selectivity of DMM and DMM2 up to 59.0% from 6.6% with a DME conversion of 8.9%; besides that, there was no COx production observed in the reaction under the optimum conditions of 513 K and 1800 h−1. The techniques of XRD, BET, NH3-TPD, H2-TPR, XPS, TEM and SEM were used to characterize the structure, surface properties and morphology of the catalysts. The optimum amount of weak acid sites and redox sites promotes the synthesis of DMM and DMM2 from DME direct oxidation.
Highlights
Dimethyl ether (CH3 OCH3, dimethyl ether (DME)) is a clean fuel with high cetane number and is a potential and non-petroleum route chemical synthesis material
The results show that the PW12 -modified Re/carbon nano-tubes (CNTs) demonstrates high activity and selectivity for the formation of DMM and DMM2 via DME direct oxidation at low temperature
The selectivity of DMM and DMM2 reaches the highest value of 59.0%, and DME conversion is increased to 8.9% when Re/CNTs is modified by 30%PW12
Summary
Dimethyl ether (CH3 OCH3 , DME) is a clean fuel with high cetane number and is a potential and non-petroleum route chemical synthesis material. Utilizing oxidation of DME to synthesize DMMx is one of the most attractive green routes for the synthesis of clean fuel additives with a short process, low CO2 emissions and high energy efficiency. A Mn-(Sm+SiW12 )/SiO2 catalyst exhibited good activity for the selective oxidation of DME to DMM at 593K, but by-product COx was usually formed due to a high reaction temperature [16]. The H3 PW12 O40 (PW12 ), which can offer acidity, was used to modify Re/CNTs. The effects of PW12 content, reaction temperature, gas hourly space velocity (GHSV), and reaction time on DME oxidation to DMMx were investigated. The results show that the PW12 -modified Re/CNTs demonstrates high activity and selectivity for the formation of DMM and DMM2 via DME direct oxidation at low temperature. There have been no reports about the DME oxidation to DMM and DMM2 over CNT-supported Re catalyst
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