Highly selective catalytic reduction of NO by H-2 over Au-0 and Au(I) impregnated in NaY zeolite catalysts

The NO-H-2 reaction has been studied over Au-0/NaY and Au(I)NaY catalysts, which were prepared by the mechanical mixing of AuCl3 with NaY zeolite and by the monolayer dispersion of Au(I) species into NaY zeolite, respectively. The precursor samples were reduced in flowing hydrogen at 423 K. The NO-H-2 reaction over these catalysts took place at relatively low temperatures under isothermal conditions from 373 to 673 K. The Au(I)/NaY catalysts were more active toward the above reaction compared with the Au-0/NaY catalysts. The NO selectivity was pointed to the N-2 and N2O formation, with the former catalysts being more selective to N-2. In situ FT-IR study of the NO-H-2 reaction on the gold catalysts demonstrated that NH3 was detected in the adsorbed NH4+ form at 1440 cm(-1), along with N2O at 2240 (2220) cm(-1) and H2O at 1645 cm(-1). Two characteristic bands due to the vibrations of N-O bond in adsorbed NO were identified. The bands at 1880 cm(-1) in the spectra of Au-0/NaY were assigned to Au-n+-NO (n approximate to 0) complexes, and the corresponding bands at 1910 cm(-1) in the spectra of Au(I)NaY were assigned to Au-n+ NO (n = 1) complexes in cages of zeolite. It was proposed that N2O and NH3 formed simultaneously at low to moderate temperatures (< 500 K) by the addition of N atom to NO and H atoms, respectively. The presence of adsorbed N atoms was confirmed by the coadsorption of NO/CO/H-2 mixture onto Au(I)/NaY at 423 K, where a band at 2280 cm(-1) ascribed to isocyanate [NCO] intermediate was developed intensively with time. This band did not deliver when a mixture of NO/CO was admitted alone to the IR cell. Therefore, the H atom promoted the N-O bond fission to form N-ad and OHad. The [NCO] species is the result of a reaction between the adsorbed N atom and gaseous CO. (C) 1996 Academic Press, Inc.