60th Annual Report on Research 2015

This research funded by ACS PRF takes advantage of a new method to control the amount, oxidation state, and nanostructuring of a transition metal deposited on a solid metal-oxide substrate. Our results suggest that copper nanostructures can be deposited on solid substrates in a chemical process where the amount of copper deposited is limited by the amount of the reducing surface sites present on a support material, and the size distribution of the nanostructures can be controlled by the deposition conditions. This research has now been completed and published (see submitted list of publications). The most attractive feature of these nanoparticles is that their core is metallic but the surface contains predominantly Cu(I) species and they can be prepared at room temperature or followed by a brief annealing to about 80°C. The nanostructures are stable in ambient conditions and withstand elevated temperatures sufficient for a chemical process to occur. The copper-based catalysts are cheap and versatile alternatives to many current systems and have high potential for applications in hydrocarbon conversion (particularly in selective oxidation) that can be used to create commodity chemicals from petroleum products.

The main questions that have been targeted within the framework of this research are related to understanding a) the reactions of dissociation and ligand displacement on the support material itself, which in most test cases is ZnO powder; b) the dissociation and decomposition pathways of common organic molecules (alkohols, acetone, acetic acid, acetaldehyde, CO, ketene) and also possible ligands that can be used for delivering copper and other metals to the substrate in a deposition process (β-diketonates and β-diketones). For example complex self-reaction of acetone was investigated and a number of long-standing controversies about this process have been addressed. The major advances have been made in understanding the reactivity of different ZnO surfaces towards dissociating an O-H bond and its competition with C-Cl dissociation, leading to the design of environmentally-friendly catalysts.

The most recent studies also address the role of copper oxidation state within a precursor molecule to control copper oxidation state in a deposited catalyst and also address the possibility of using very low temperature annealing (about 80°C) to remove the ligands from nanoparticles and place them on a support material instead. This is the first report of using such a low-temperature transmetalation process to prepare metal catalyst on an oxide surface that may be further generalized to other metals and other support materials.

Since thermal desorption is one of the main methods used in these and previous studies, it is worth mentioning that a methodological approach used to decipher complex thermal desorption traces is being transferred to allow general users to follow the directions for data treatment, the methodological proposal supported by the National Science Foundation (the research is now completed). However, some of the test systems and reactions are investigated within the framework of this grant; thus the resulting publications will acknowledge both contributions.