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The catalytic behaviour of a CuZnZr-FER hybrid catalyst was assessed in the direct CO 2 -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 (T R  = 220–260 °C; P R  = 3.0 MPa; GHSV = 8800 N L/kg cat /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. [ABSTRACT FROM AUTHOR]

The catalytic behaviour of Cu-Zn-Zr/zeolite hybrid systems, in which metallic and acidic functionalities were combined at level of single grain, was evaluated in the direct DME production by CO 2 hydrogenation. Catalysts were prepared by co-precipitation of the metals precursors in a slurry of three home-made powdered zeolites, characterized by different dimensional frameworks ( i.e. , MOR, FER, MFI). The experiments were carried out in a fixed bed reactor operating at 5.0 MPa and temperature ranging from 200 to 260 °C. By appropriate physico-chemical characterization of systems it was revealed that morphology of zeolite crystallites significantly affects the surface distribution of metal-oxides and the nature of active sites created during the co-precipitation step. The FER zeolite was seen to ensure a better dispersion of cluster oxides, favouring the generation of Lewis basic sites for CO 2 activation along with a higher availability of Brønsted acid sites for the MeOH-to-DME dehydration step. The catalytic results clearly evidenced a net difference in behaviour among the investigated hybrid systems, both in terms of CO 2 conversion and product distribution. Peculiar structure-activity relationships highlighted the superior performance of CuZnZr-FER catalyst, allowing to reach the highest DME productivity value (≈600 g DME /kg cat /h), as the consequence of better efficiency in mass transferring ensured by neighbouring active sites involved in the reaction mechanism. The stability test evidenced a progressive deactivation not associated to coke deposition or metal sintering, but mainly to water formation which negatively affects the behaviour both of metal-oxide and acid sites controlling the DME synthesis rate. [ABSTRACT FROM AUTHOR]

Deactivation rate and interface metal-to-zeolite contact area (θ M/Z). • Six home-made zeolites were embedded in catalyst composition for direct CO 2 -to-DME hydrogenation. • All the hybrid catalysts exhibited a specific loss of activity during the early phase of reaction. • Neither hydrocarbon or coke formation, nor metal sintering were responsible for the decay of activity. • A linear relationship was found between the deactivation rate and the population of weak acid sites. • A lower framework density of the zeolite structure is fundamental for a larger interface area with the metal-oxide sites, so leading to more stable catalysts. • Zeolite framework density controls the extent of interface area with the surface sites as well as catalyst stability. A significant boost to the catalytic technology of CO 2 -to-DME hydrogenation in a single step was recently given by the design of novel hybrid multimetallic/zeolite systems. However, a significant drop of catalyst activity after few hours of operation time pushes now the research interest towards the development of more stable multifunctional systems, suitable to ensure activity, selectivity and lifetime under typical industrial conditions. In this work, the influence of different home-made zeolite samples (i.e. , Sil-1, MFI, Y, FER, BEA, MOR), integrated in a weight ratio of 1:1 with a CuO-ZnO-ZrO 2 metal-oxide(s) phase, was investigated under long-term stability tests in a fixed bed reactor during CO 2 hydrogenation reaction to assess the activity-selectivity pattern of the hybrid catalyst as well as their deactivation trend during operation time. The individuation of key structure-activity relationships helped to explain how the extent of interaction between the metal-oxides phase with the zeolite surface as well as the strength of the acid sites significantly control the catalyst stability. [ABSTRACT FROM AUTHOR]