Cu/ZnO and Cu/ZrO₂interactions studied by contact angle measurement with TEM

Abstract

A technique of contact angle measurement was applied to the nano-scale oxide-supported metal particles. For Cu supported on ZnO and ZrO2 the angles were found to increase and the work of adhesion to decrease with increasing particle size. Such a trend is interpreted as an effect of negative contact line tension of 2.1 x 10(-9) J m(-1) and 1.0 x 10(-9) J m(-1) in the Cu/ZnO and Cu/ZrO2 system, correspondingly. For the small-sized Cu particles the apparent work of adhesion on ZnO support is higher than that on ZrO2.

Ambient pressure photoelectron spectroscopy: A new tool for surface science and nanotechnology

“…The very rich defect chemistry of ZnO [75] allows for such subtle distinctions. The assumption of different defect states of ZnO filling the spaces between particles and on the Cu particles helps explain the apparent discrepancy of the present model with the observations by electron microscopy [76] of a weak wetting interaction between Cu and ZnO without mentioning the possibility of its coexistence with a strongly wetting component of ZnO. Here the in-situ XPS provides complementary insight of a thin and strongly wetting ZnO that would not be visible in the TEM.…”

Electron Microscopy of Solid Catalysts—Transforming from a Challenge to a Toolbox

“…As shown, for example, on Cu particles supported on ZnO or ZrO 2 for methanol synthesis, contact angles between particles and support (wetting effect) are measured based on electron micrographs (Figure 29a−m). 325,376 On both supports, the contact angles depend on the Cu particle size, but not linealy. They reach a stable value around 120°at the Cu equivalent diameter of about 6 nm (Figure 29o).…”

Neural Network Potential Simulations of Copper Supported on Zinc Oxide Surfaces

“…6.2.5), by showing changes in the inter-atomic distances that reach the uppermost layers of the clusters far from the interface even for the largest sizes. The straining of the clusters could have consequences on the behavior of the supported clusters in experimental and reaction conditions, since many experimental studies of the industrial catalyst highlight the correlation between strain and reactivity [16,17,27]. The simulations also reveal the formation of multiple fcc domains separated by hcp regions (sec.…”

“…The industrial catalyst itself is usually prepared [12][13][14] by mixing the inorganic nitrate salts of Cu (in the highest proportion), Zn, and Al, co-precipitating with sodium carbonate, followed by steps of ageing, drying, calcination, reduction, and annealing at high temperature. Many atomic microscopy images of the commercial catalyst with techniques such as transmission electron microscopy (TEM) and scanning tunneling microscopy (STM) are available [15][16][17][18][19], revealing a complex mixture of Cu and ZnO nanoparticles. Most of the nanoparticles can be distinctly identified as being either copper or zinc oxide, but the particles are often stuck to one another, and even at this scale the structure of the interface between the materials is hard to discern.…”

“…To mention a few of the more relevant theories, it has been proposed that ZnO: i. serves as a storage of hydrogen that then reacts on the copper [21] ii. induces and stabilizes strain and defects on the copper which enhances the catalytic activity of the copper phase [16,17,27], while also preventing coalescence of the nanoparticles and thus increasing the Cu surface area [10] iii. provides oxygen atoms to form a mixed copper oxide phase that is assumed to be the active material [28] iv.…”