Nonprecious catalytic honeycombs structured with three dimensional hierarchical Co3O4 nano-arrays for high performance nitric oxide oxidation

Abstract

A new type of noble metal-free catalytic honeycomb has been successfully developed by rational assembly of hierarchical Co₃O₄ nano-arrays on three dimensional ceramic honeycomb substrates. Different cobalt precursors were found to induce different assembly fashions for Co₃O₄ nano-array growth. Different Co₃O₄ growth mechanisms including “dumbbell aggregation” and “elongation–splitting” have been proposed to interpret the morphology evolution. The Co₃O₄ nano-array based catalytic honeycombs exhibit high performance catalytic NO oxidation with conversion efficiency as high as 80% at 275 °C. Such catalytic honeycombs were able to sustain their high NO conversion under either cyclic or long term steady isothermal operation and demonstrate excellent temperature fluctuation adaptability. The NO conversion capability of Co₃O₄ nano-arrays was determined by the amount of Co³⁺ on the surface, which acts as the active sites. Increased surface area enabled by small grain size and porous nature of nanowires promotes low temperature NO conversion. Thermal annealing at different temperatures was demonstrated to tune the porosity, grain size and thus the surface area of Co₃O₄ nano-arrays, which further influence the catalytic activity.