Abstract
The water gas shift (WGS) reaction is widely used in the production of hydrogen, by the conversion of carbon monoxide into CO2 and of water into H2. In the present work, copper catalysts supported on alumina or carbon nanofibers (CNF) were used to study the WGS reaction. The catalysts were prepared by impregnating coppernitrate in the supports, with a nominal mass metallic content of 5%. The solids were dried, calcined and characterized by X-Ray Diffraction (XRD), nitrogen adsorption, nitrous oxide chemisorption and Inductively Coupled Plasma Optical Emission Spectrometry (ICP OES).
After calcination, the catalysts were loaded into the reactor, reduced and then tested in the WGS reaction at medium temperatures (398 – 573 K). The gases from reactor were analyzed online by Gas Chromatography (GC). The products were CO2, H2 and, probably, small amounts of coke. The CO partial pressure varied between 4.6 and 6.6 kPa, and the water partial pressure varied between 20.0 and 47.4 kPa.
Among the catalysts tested, 5% Cu/Al2O3 was the most active under all conditions used in this work, due tothe high dispersion of the metal particles on the support. The most favorable reaction conditions for this catalyst were p0H2O= 38.6 kPa and p0CO= 5.3 kPa (H2O:CO molar ratio of 7.3), for all reaction temperaturesused in this work. Cu/CNF had low CO conversions, due to the support hydrophobicity. In case of this catalyst, the most favorable conditions were p0H2O= 20.0 kPa and p0CO= 6.6 kPa, corresponding to a H2O:CO molar ratio of 3.1. The apparent activation energy calculated for the WGS reaction was 86.1 kJ mol-1 for 5% Cu/Al2O3 and 69.8 kJ mol-1 for 5% Cu/CNF. For Cu/CNF a co-operative redox reaction mechanism was proposed, andapparent reaction orders were 0.64 in relation to CO and approximately zero in relation to water.
