Dynamical Changes in the Cu–ZnO x Interaction Observed in a Model Methanol Synthesis Catalyst

Abstract

A systematic series of model methanol synthesis catalysts was prepared by sequential impregnation of a mesoporous silica material (5 nm average pore size) with an organometallic ZnO precursor which is liquid at room temperature, followed by the infiltration with an aqueous Cu nitrate solution. These catalysts, which contained 14-20 wt.% Cu and 1-5 wt.% Zn, were characterized by N 2 O reactive chemisorption, by EXAFS and by measuring their methanol synthesis activities. It was observed that the formation of confined, nanocrystalline ZnO prior to copper infiltration is of major importance for the development of catalyst activity. Severe reduction of properly prepared catalysts (10% CO/H 2 , 673 K, 15 min) leads to the emergence of a new feature in the ZnK EXAFS spectrum which was assigned to a Cu neighbour by combined evidence from the ZnK EXAFS and XANES regions. The zinc oxide component was partially reduced as well, but Zn(0) was not formed to any significant extent. Catalysts which developed this Cu-Zn 2? interaction under severe reduction were superior in terms of methanol synthesis rate per m 2 Cu surface area to a sample which did not exhibit this feature.

Methanol synthesis over Cu–ZnO aggregates supported on carbon nanotubes

“…However, it has been shown earlier that such a situation can also occur in samples where Zn is unreduced [3]. This was interpreted as evidence for a SMSI situation where oxygen-depleted zinc oxide moieties migrate onto the surface of Cu crystallites [12][13][14].…”

“…We are herein presenting a study on structure and methanol synthesis activity of Cu/ZnO clusters supported on or deposited into multi-walled carbon nanotubes (CNTs). This work was part of our program to study the Cu-ZnO interaction by using model catalysts containing both components hosted in mesopore systems [2,3]. While our effort to introduce CuO and ZnO into the interior space of small-diameter CNTs [4] was inspired by reports on electronic confinement effects within the tubes [5,6], the observation of favorable effects of CNTs in higher alcohol synthesis from syngas [7] prompted us to also include catalysts with the active components deposited on the exterior surface and within the interior of wide CNTs.…”

Interplay between pore size and nanoparticle spatial distribution: Consequences for the stability of CuZn/SiO2 methanol synthesis catalysts

“…The lower than expected areas for catalysts supported on SG5 might relate to the blockage of a larger fraction of the metal surface area by direct contact with the silica pore walls, due to the similar dimensions of the Cu nanoparticles and the silica mesopores [61].…”

Heterogeneous Catalysis

“…Especially the latter has not yet been investigated to a large extent because a structural rigidity is usually assumed, the narrow limitations of which will now be discussed. Furthermore, the molecular processes of activation and deactivation are only understood in exceptional situations50b,f,j, 54a, 264a, 267 and can, therefore, seldom be treated conceptually.…”