Carbon Nanotubes-γ-alumina Composite Supported Pt-Ni Catalysts For Preferential Oxidation Of CO In H₂-rich Gases

Among those methods for removal of CO from a H2-rich stream, thepreferential oxidation of CO (CO-PROX) had been supposed to be one of the mostpromising methods. Pt-based catalysts possess high activity, selectivity and stabilityin practical application for CO-PROX reaction, while their low temperature catalyticperformance is needed to be further improved. CO oxidation is an exothermicreaction which may lead to generate hotspots in the catalysts, and reverse water gasshift (RWGS) reaction may be induced on these hotspots. RWGS reaction isendothermic and produces CO thus influencing the net removal of CO. To solve theabove problems, in this work, the Pt and Ni were used as active components, CNTsdoped alumina composite material was used as supports. A series of Pt-Ni bimetalliccatalysts were prepared for CO-PROX. Through investigating the doping amount ofCNTs, differences in active component and supports for the effect to theperformance of the catalyst. This work is to develop a novel catalyst with highcatalytic performance for the preferential oxidation of CO.The carbon nanotubes (CNTs)-γ-alumina composite was prepared by colloidalprocessing. A series of CNTs-γ-alumina composite supported platinum-nickelcatalysts were prepared by co-impregnation method and were applied to thepreferential oxidation (PROX) of CO in H2-rich gases. Through H2-TPRcharacterization, N2adsorption-desorption and the performance test of catalysts, itcan be found that when the loading of Pt and Ni was controlled at1wt%and1.5wt%, respectively and the amount of doped CNTs was5wt%, the catalyst achievethe optimal performance.1%Pt-1.5%Ni/5%CNTs-γ-Al2O3exhibited complete COconversion in the temperature range of70to110°C in1vol.%CO,1vol.%O2,50vol.%H2and N2(balance) at mass space velocity of24,000ml·gcat-1·h-1. As reactiontemperature increased to130°C, CO conversion slightly decreased and the outletCO concentration was10ppm. When the reaction temperature increased to150°C,the CO conversion decreased to some extent, and the residual CO concentration was 90ppm. The selectivity of O2to CO oxidation maintained at around51.3%.In order to further study the relationship between structure and catalyticperformance of the catalysts1%Pt-1.5%Ni/5%CNTs-γ-Al2O3. The catalysts werecharacterized by using N2adsorption-desorption, X-Ray diffractions (XRD),H2-temperature programmed reduction (TPR), transmission electron microscopy(TEM), scanning transmission electron microscopy (STEM) and scanning electronmicroscopy (SEM). The Pt-Ni alloy species which can be reduced at lowtemperature are highly dispersed on the support. CNTs in the composite werewrapped and the nanoparticles of Pt-Ni were on the surface of Al2O3. The very goodcatalytic performance of this catalyst is attributed to the formation of Pt-Ni alloy aswell as the addition of CNTs, which can avoid or mitigate the formation of hotspots.The hotspots can increase the selectivity of oxygen to H2oxidation and can generatereverse water gas shift reaction, both of which are harmful for eliminating CO.