메탄 산화를 위한 Pd 촉매의 특성

Abstract

The reaction properties of Pd. Pd-Ce and Pd-La catalysts supported on γ-Al2 were investigated in the oxidation reaction of methane(CH4) exhausted from the compressed natural gas vehicle in a U-tube flow reactor with gas hourly space velocity of 72,000 h-1. The catalysts were characterized by X-ray diffraction(XRD), X-ray photoelectron spectroscopy(XPS), BET surface area and hydrogen chemisorption. Pd catalyst prepared by Pd(NO3)2 as a palladium precursor and calcined at 600 ℃ showed the highest activity for a methane oxidation. Catalytic activity of calcined Pd/γ-Al2O3 in which most of palladium was converted into palladium oxide species was higher than that of reduced Pd/γ-Al2O3 in which most of palladium existed in palladium metal by XRD. As increasing the number of reaction cycles in the wide range of redox, the catalytic activity of Pd/γ-Al2O3 was decreased and the highly active window became narrower. Lanthanum oxide promoted Pd catalyst, Pd/La/γ-Al2O3 showed enhanced thermal stability compared with Pd/γ-Al2O3 even after aging at 100 ℃, which was ascribed to the role of La as a promoter to suppress the sintering of palladium metal and γ-Al2O3 support. Almost all of methane was removed by the reaction with NO at the redox ratio of 1.2 in case of oxygen excluded steam, but that activity was significantly decreased in the steam containing oxygen.