ORIGINAL PAPER Effect of Fe on the activity of Au/FeO x -TiO 2 catalysts for CO oxidation Mpfunzeni Raphulu 1 & Thabang Ntho 1 & Pumeza Gqogqa 1 & John Moma 1 & Lebohang Mokoena 1 & Gary Pattrick 1 & Mike Scurrell 3 & Laurent Delannoy 2 & Catherine Louis 2 Received: 14 October 2015 /Accepted: 9 February 2016 # Springer International Publishing Switzerland 2016 Abstract A thorough characterisation of Au/TiO 2 and Au/ FeO x -TiO 2 catalysts was conducted in order to get a better understanding of the effect of Fe on the Au/TiO 2 catalysts and link it to differences observed in their activities for CO oxidation. Several techniques including HRTEM, temperature-programmed reduction (TPR), UV-Vis and temperature-programmed desorption (TPD) of isopropyl amine, CO and CO 2 were used to characterise the catalysts. Au/FeO x -TiO 2 (300 °C), which was found to be the most active catalyst for CO oxidation, had the highest number of Brønsted acid sites, although its concentration of Lewis acid sites was similar to all other tested catalyst systems. X-ray photoelectron spectroscopy (XPS) revealed that the Fe species on the Au/FeO x -TiO 2 catalyst is Fe 2+ with a very small amount of Fe 3+ . Fe 2+ is comprised of both FeO and Fe 3 O 4 species, and according to TPR, the ratio (FeO/Fe 3 O 4 ) between these two species increases with increasing calcination tem- perature. The presence of Fe on the Au/TiO 2 catalyst seems to stabilise the Au nanoparticles from agglomeration. The acti- vation energy of desorption (E d ) of CO from Au/FeO x -TiO 2 (300 °C) was 82.7 kJ/mol, whilst on Au/TiO 2 , the E d for CO was 108.8 kJ/mol. On both catalysts, the E d for CO 2 was ca. 99 kJ/mol. Keywords Gold . Catalysts . Oxidation . CO . Titania . Iron oxide Introduction The Au/TiO 2 catalyst is one of the most studied systems for the oxidation of carbon monoxide. It has been reported to be a highly active catalyst, although it undergoes deactivation with time online like many other studied catalysts. Deactivation of gold catalysts is a drawback that can possibly delay the pro- duction of Au-based technological products [1]. Deactivation of supported gold catalysts during CO oxida- tion has been ascribed to various factors such as change in oxidation state of gold [2, 3] and aggregation/sintering of the gold nanoparticles [4] as well as other morphological changes on both the support and the metal [5]. Another commonly suggested cause of deactivation is the formation and accumu- lation of carbonaceous (or carbon-containing) species such as carbonates, bicarbonates and formates on the surface of the catalyst [6]. The complexity of the deactivation of gold cata- lyst is brought about by the fact that all or most of the deactivating factors might be occurring simultaneously. For example, Konova et al. [7] found evidence of carbonate accu- mulation and gold agglomeration during CO oxidation catalysed by Au/ZrO 2 and Au/TiO 2 , observing that the two processes have different effects. Sintering of gold particles caused an irreversible deactivation, but these effects are usu- ally small with most catalysts retaining their activities as long as the average gold cluster is retained within the 2–5 nm di- ameter range. The accumulation of carbonaceous species, on the other hand, may lead to a significant activity loss by blocking the active sites [8], although the effect can be re- versed by removal of these species by treatment in inert gas at temperatures up to 573 K. It has also been reported that * Thabang Ntho thabang.ntho@mintek.co.za 1 Project AuTEK, Advanced Materials Division, Mintek, Private Bag X3015, Randburg 2125, Republic of South Africa 2 Laboratoire de Réactivité de Surface, UMR 7197 CNRS, Université Pierre et Marie Curie-UPMC, 3 rue Galilee, 94200 Ivry, France 3 Department of Civil and Chemical Engineering, University of South Africa, P.O. Box UNISA, Pretoria 0003, South Africa Gold Bull DOI 10.1007/s13404-016-0178-4