Systematic Catalyst Screening of Zeolites with Various Frameworks and Si/Al Ratios to Identify Optimum Acid Strength in OME Synthesis

Abstract

Oxymethylene dimethyl ethers (OMEx oligomers with the chain length x) present a promising emission reducing diesel additive, which can potentially be produced based on renewable resources. In this work, the OMEx synthesis catalysed by zeolites was investigated starting from paraformaldehyde and methanol. The catalytic performance of zeolites with different framework types (BEA, FAU, MFI, MOR) and various Si/Al ratios was comparatively studied. The zeolites were characterised by means of NH3-TPD, ICP-OES, XRD and N2 physisorption. A relationship between catalytic activity and Si/Al ratio was established demonstrating the highest turnover frequency for zeolites with high Si/Al ratios. HZSM-5 114 with a TOF of 3375 molOME3–5 molAcidSites−1 h−1 was determined as the best-performing zeolite which indicates that the OMEx synthesis requires a moderately strong acid strength.