Gold, silver and copper catalysts supported on TiO2 for pure hydrogen production
Introduction
The water gas shift reaction (WGSR) is one of the oldest methods for pure hydrogen production. Recently, the interest to WGSR has been renewed due to the possibility to use pure hydrogen in fuel-cells or in other reactions related to environmental protection and clean technologies.
Copper-based catalysts are well known low temperature WGSR catalysts [1]. Quite recently, it was established that also nano-sized gold catalysts supported on TiO2 and Fe2O3 are very active at low temperatures in the WGS reaction [2]. Some results, concerning a FTIR study of WGS reaction on Au/TiO2 and Au/Fe2O3 catalysts, have already been reported by some of us [3]. Here a comparative study of IB metals on titania will be presented. The chemisorption and catalytic properties of the IB metals have been already the object of some comparative studies [4]. In this paper, we will present a TPR, FTIR and catalytic study mainly devoted to understand the strong differences in the catalytic activity of the three title catalysts in the hydrogen production by CO WGSR.
Section snippets
Materials
The samples were prepared by the deposition–precipitation method [2] in a ‘Contalab’ laboratory reactor (ContravesAG, Switzerland) under complete control of all parameters (temperature, pH, stirrer speed, reactant feed flow rates, etc.). The deposition–precipitation method involves the deposition on titania, preliminarily suspended in water by the ultrasounds technique, of the corresponding metal hydroxide or hydrocarbonate through chemical interaction of initial metal salts and Na2CO3 in
Catalytic activity
The catalytic activity data are summarised in Fig. 1. The samples were reduced in a 1% H2 in argon feed, at 493 K as for the Cu/Ti sample and at 373 K as for the Au/Ti and the Ag/Ti samples, before the measure. The silver catalyst remains almost completely inactive in all the examined temperature range, with a maximum conversion of 6% at 520 K, while gold gets a CO conversion of 80% at the same temperature and copper exhibits an intermediate behaviour, by getting a 30% conversion. We have
Conclusions
From the comparative study of the three IB metals nano-dispersed on titania it can be concluded that:
- •
The gold reduced catalyst activates CO molecules on surface step sites. The FTIR absorption band red-shifts if CO or water are coadsorbed on the support cations. The red-shift of the band may be ascribed to an electronic effect of coadsorbed species. This mutual effect, evidenced by the FTIR technique, can be also at the origin of the enhanced reactivity of water and CO already discussed or
References (22)
- et al.
Appl. Catal. A
(1996)et al.Bulg. Chem. Comm.
(1998) - A. Baiker, M. Kilo, M. Maciejewski, S. Menzi, A. Wakaun, in: L. Guczi, et al. (Eds.), New Frontiers in Catalysis,...
- et al.
Appl. Catal. A
(1992) - et al.
J. Catal.
(1997) - et al.
Appl. Catal. A
(1999) Appl. Catal. A
(2000)- et al.
J. Catal.
(2001) - et al.
J. Phys. Chem.
(1996)G.C. Bond, D.T. Thompson, Catal. Rev. Sci. Eng. 41 (1999) 319 and references... - et al.
Mater. Chem. Phys.
(1991) - et al.
Surf. Sci.
(1998)