Understanding and Optimizing the Performance of Cu-FER for The Direct CH4 to CH3OH Conversion

Cu-exchanged zeolites with the Ferrierite topology were investigated in the direct CH4 to CH3OH conversion. Samples with a systematic compositional variation in terms of Na/Al and Cu/Al ratios where synthesized by liquid ion exchange. The presence of Na is observed to be beneficial for the Cu exchange and thereby higher Cu loadings were achieved. The overall performance of Cu-FER samples depends on Cu loading as well as the conditions of the reaction. Elevated O2 activation temperature as well as long CH4 loading times are proven to enhance the CH3OH yield of the Cu-FER sample with Cu/Al=0.2. In addition, the productivity depends on the Cu/Al ratio, at low values the sample is almost inactive indicating a Cu threshold that needs to be surpassed. We employed X-ray absorption and IR of adsorbed CO spectroscopies in order to rationalize the performance as well as the effect of Cu/Al ratio. From the in situ spectroscopies we ultimately establish structure-activity relationships between the reducibility of Cu species and the CH3OH yield.