Preferential oxidation of CO in H2/H2O/CO2 water–gas shift feedstocks over Cu-based carbon nanotubes-supported heterogeneous catalysts

Abstract

Selective carbon monoxide (CO) oxidation reaction was studied over mono- and bimetallic Co, Cu and Fe, as well as Cu–Co and Cu–Fe heterogeneous catalysts, using multi-walled carbon nanotubes (MWCNT) as substrates. Materials were synthesized by wet (co-)impregnation technique and characterised. It was found that hydrophilic hydroxyl and carboxyl nanotubes’ (CNT) functional groups were favourable for a strong metal–support interaction. The catalytic conversion performance for preferential CO oxidation (PROX) process was carried out in hydrogen, water, and carbon dioxide-containing feedstock gasses. The addition of iron or cobalt to Cu/CNT improved the activity with comparison to Cu/CNT. The optimized Cu–Fe/CNT could preferentially oxidize dilute CO in H2-rich simulated WGS streams within a wide temperature range of 120–220 °C. The temperatures, where 50% CO conversion was achieved, were as follows: Cu–Fe/CNT (120 °C) > Cu–Co/CNT (140 °C) ≈ Cu/CNT (140 °C). A high determined selectivity towards CO2 for Cu–Fe/CNT could be attributed to the presence of CuFe2O4 and the synergy between Co and Cu for Cu-Co/CNT. At 220 °C and in a 1% CO/1% O2/10% H2O/10% CO2/60% H2/18% He stream, Cu–Fe/CNT could achieve a 100% CO conversion, granting a low H2 conversions, not differing from those in the absence of CO2, while its turnover performance remained stable for a longer continuous time-on-stream with basically no deactivation. By comparison, Cu–Fe/CNT exhibited a higher apparent rate and lower activation energy of CO conversion (with and without H2O and CO2).