Oxidation and reduction in copper/zinc oxides by mechanical milling

Abstract

When zinc oxide is milled under vacuum or in the presence of oxygen, creation of various types of defects results in an increased amorphous fraction, as well as higher surface area. Mechanochemical reactions occur when copper and copper oxides are milled together with zinc oxide: oxidation of copper and copper oxides takes place in the presence of oxygen, whereas reduction takes place under vacuum. These reactions are promoted by the presence of ZnO. Formation of a Cu 2 O-like intermediate is suggested, which is not observed when milled without ZnO. The various resulting copper species reduce at different temperatures in H 2 atmosphere. Both Cu 0 specific surfaces and BET surfaces are substantially increased for all milled Cu/ZnO samples, making this method an interesting alternative for the preparation of promoted heterogeneous catalysts.

Cation substitution in ZnO obtained by mechanical milling

“…The typical grain size reduction with milling occurred from the initial value of 100 nm to around 30 for both samples. Similar grain size reduction was observed in pure milled ZnO [8][9][10]. The decreasing fraction of the minor oxides with milling time is also shown in Table 1.…”

Modification to the composition of nanocrystalline RuO2 through reactive milling under O2

“…In the case of RuO 2 , these oxygen vacancies result in Ru moieties that are not fully coordinated with oxygen. The creation of oxygen vacancies during the milling of oxides has already been suggested to explain several properties of the resulting materials [10,35]. Oxy- gen vacancies present on freshly exposed ruthenium oxide surfaces will tend to increase their surface energies.…”

“…A variety of materials have been prepared by milling powders under hydrogen (metal hydrides), oxygen (metal oxides), nitrogen (TiN), and even ammonia (boron and silicon nitrides) [7][8][9][10][11][12][13]. Increase of surface area by milling under a reactive atmosphere (O 2 ) has been reported for some metal oxides [10]. Here, we have investigated milling of RuO 2 powders under an oxygen atmosphere as a way to increase surface area (m 2 /g) and specific charge (C/g).…”

New Highly Mixed Phases in Ball-Milled Cu/ZnO Catalysts as Established by EXAFS and XANES

“…As an alternative to the usual coprecipitation methods used to prepare highly mixed catalyst systems, a mechanochemical method can be applied that additionally allows solid-state reactions between the individual particles as well as reactions with the gas atmosphere. Consequently, by ball milling of CuO x /ZnO mixtures, intimately mixed precursors may be produced for the highly active methanol synthesis catalyst [1,2]. In order to unravel the complex structures of a series of systems obtained after ball milling Cu 2 O/ZnO in different atmospheres, a XAFS investigation has been carried out at both the Cu and Zn K-edge.…”