Tuning catalysis by surface-deposition of elements on oxidation catalysts via atomic layer deposition

Abstract

Based on the concept that most reaction steps proceed only at the surface layer of a bulk catalyst, the catalytic impact of the surface-modification with PO_x, BO_x, and MnO_x in the selective oxidation of ethane, propane, and n-butane is systematically studied. Three different promoter elements are deposited as a sub-monolayer on the surface of oxidation catalysts with high dispersion by sequential and self-limiting reactions at the solid–gas interface, using atomic layer deposition. Oxygenate and olefin selectivities are tuned by the surface deposition of PO_x and BO_x, leading to improved product yields. The mixed metal oxide MoVTeNbO_x is used as a case study to demonstrate the effect of the modification in different reactions with yield improvements of up to 24% in the propane oxidation towards acrylic acid. It is shown that the beneficial performance is related to a change in surface composition, a modification in the electronic properties of the redox active element vanadium, and a decrease in acidity. A comparative study considering several bulk catalysts and deposited elements revealed further promoting effects for different oxidation catalysts. In particular, the deposition of PO_x on V-containing oxides suppresses CO_x formation. Precisely adjusted surface modifications leading to enhanced product yields demonstrate the potential of atomic layer deposition as a powerful tool for tuning catalytic properties of bulk catalysts.