Highly Selective Catalytic Reduction of NO by H2over Au0and Au(I) Impregnated in NaY Zeolite Catalysts

The NO–H2reaction has been studied over Au0/NaY and Au(I)/NaY catalysts, which were prepared by the mechanical mixing of AuCl3with 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–H2reaction 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 Au0/NaY catalysts. The NO selectivity was pointed to the N2and N2O formation, with the former catalysts being more selective to N2.In situFT–IR study of the NO–H2reaction on the gold catalysts demonstrated that NH3was detected in the adsorbed NH4+form at 1440 cm−1, along with N2O at 2240 (2220) cm−1and 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−1in the spectra of Au0/NaY were assigned to Aun+–NO (n ≈ 0) complexes, and the corresponding bands at 1910 cm−1in the spectra of Au(I)/NaY were assigned to Aun+NO (n = 1) complexes in cages of zeolite. It was proposed that N2O and NH3formed 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/H2mixture onto Au(I)/NaY at 423 K, where a band at 2280 cm−1ascribed 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 Nadand OHad. The [NCO] species is the result of a reaction between the adsorbed N atom and gaseous CO.