Acidity control of zeolite functionality on activity and stability of hybrid catalysts during DME production via CO2 hydrogenation

The catalytic behaviour of a CuZnZr-FER hybrid catalyst was assessed in the direct CO2-to-DME hydrogenation reaction, considering the effects of structural and surface properties induced on the system by homemade ferrierite samples at different acidity and grain size. Notwithstanding a comparable initial activity under the adopted experimental conditions (TR = 220-260 °C; PR = 3.0 MPa; GHSV = 8800 NL/kgcat/h), the investigated catalyst samples exhibited a different behaviour in terms of stability, with a progressive decay with time mostly marked on the hybrid containing ferrierite at larger acidity. Irrespective of the zeolite grain size, TEM analysis showed a low tendency of catalysts to form carbon deposits, while the comparison of surface properties of “fresh” and “used” samples evidenced a significant metal sintering occurring during reaction, proportional to the Si/Al ratio. The loss of metallic surface area was mainly connected to water formation, as proved in the measurements at high contact time in which a larger net drop between initial and final DME yield, resulting from a higher partial pressure of water, was recorded.