Elucidating elementary processes at Cu/ZnO interfaces: A microscopical approach

Abstract

Despite its enormous importance for heterogeneous catalysis, and in particular methanol synthesis, detailed information about the Cu/ZnO interface is still far from being complete. Here we present an overview of recent work carried out using different types of microscopical methods from which the complexity of the problem becomes apparent. In addition to results from transmission electron microscopy (TEM) and scanning electron microscopy (SEM) data also obtained using scanning probe techniques, in particular scanning tunneling microscopy (STM) and atomic force microscopy (AFM) are presented. Special attention is paid to the influence of elevated temperatures on the Cu/ZnO interface.

Synthesis of Cu, Zn and Cu/Zn brass alloy nanoparticles from metal amidinate precursors in ionic liquids or propylene carbonate with relevance to methanol synthesis

“…{[Me(C(N i Pr) 2 )]Cu} 2 (1) and [Me(C(N i Pr) 2 )] 2 Zn (2) were synthesized by deprotonation and methylation of 1,3-diisopropylcarbodiimide with methyllithium. The resulting lithium amidinates were then reacted with copper(I) or zinc(II) chloride according to literature procedures.…”

“…The amidinates {[Me(C(N i Pr) 2 )]Cu} 2 (1) or [Me(C(N i Pr) 2 )] 2 Zn (2) were dissolved/suspended under a nitrogen atmosphere in dried and deoxygenated 1-butyl-3-methylimidazolium tetra-uoroborate ([BMIm][BF 4 ]) or propylene carbonate (PC). Complete decomposition by microwave irradiation of the amidinates in these solvents was achieved aer only 10 minutes using a low power of 50 W to give an approximate temperature of 220 C in the reaction mixture (Scheme 3).…”

“…Cu/ZnO nanocomposite systems have been studied in great detail over many years in order to elucidate the elementary processes of relevance for heterogenous catalytic methanol formation from CO/CO 2 /H 2 mixtures. 1 Nevertheless, the role of Cu, ZnO and the Cu/ZnO interface is still a matter of ongoing research and important factors include the decoration of Cu nanoparticles with Zn and ZnO species. 2 Bottom-up synthesis and microstructural characterization of free-standing Cu/ZnO composite nanoparticles dispersed in non-aqueous media and their investigation as quasi-homogeneous model catalysts have contributed to this discussion.…”

“…8, 9 Herein we wish to report related, new results employing a different metal-organic precursor concept and using the advantages of the synthesis of nanomaterials in ionic liquids or propylene carbonate (PC) to selectively yield the intermetallic nano-brass phases b-CuZn and g-Cu 3 Zn as stable colloids. We selected the copper(I)-amidinate {[Me(C(N i Pr) 2 )]Cu} 2 (1) and the related zinc(II)-amidinate [Me(C(N i Pr) 2 )] 2 Zn (2) (Scheme 1) as precursors for the Cu and Zn components. Metal amidinates were investigated and widely used as precursors for thin metal lms in low pressure chemical vapor deposition (CVD) or atomic layer deposition (ALD).…”

Enhanced wetting of Cu on ZnO by migration of subsurface oxygen vacancies

“…The growth of Cu on the polar ZnO(0001) surface 24 25 26 , as well as thermally induced effects 27 28 29 30 31 32 33 have been the subject of extensive debate and have also been intensively investigated theoretically 34 35 36 . Previous investigations on Cu/ZnO(0001) (refs 31 , 33 ) left several important questions about the thermally induced behaviour of this system, such as disappearance of 3D-like Cu NPs 31 , Cu-induced changes of the ZnO surface structure 31 and Cu–Zn alloying 37 38 upon annealing, unanswered.…”