Redox behavior of transition metal ions in zeolites. I. Reversibility of the hydrogen reduction of copper Y zeolites

Abstract

Publication costs assisted by the National Science Foundation (USA) and the National Fonds voor Wetenschappelijk Onderzook (Belgium)The reduction of Cu(II) ions in CuNaY zeolites occurs via a two-step mechanism in which Cu(I) is first formed and then reduced to metallic copper. The first step in the reduction may be carried out by using relatively mild conditions, e.g., H2 at 200°C for 1 hr, and it is completely reversible. Reduction in H2 at 400°C results in the formation of copper crystallites, some of which grow to a size of 300 Á after 20 hr of reduction. The copper in these larger crystals may be reoxidized slowly to CuO. The smaller metal particles, which are postulated to reside within the zeolite cages, may be readily reoxidized to Cu(II), located at exchange sites within the zeolite. Approximately half of the metallic copper is in the form of the larger crystallites and half is present in small clusters. The reduction and reoxidation was followed by quantitatively observing the H2 or O2 consumption and H2O produced in the reaction, while the amount of Cu(II) was determined by EPR spectroscopy. The presence of Cu(I) was detected by the ir and EPR spectra of the Cu+-CO and Cu+-NO complexes, respectively.

Selective Catalytic Reduction of NO by NH3 on Cu-Faujasite Catalysts: An Experimental and Quantum Chemical Approach

“…After outflowing with pure He at (16,32) and He (4) were followed. The concentrations were derived from intensities by using prior standardisation procedures.…”

Fe/ZSM-5 zeolites for organic-pollutant removal in the gas phase: Effect of the iron source and loading

“…This effect occurs because of the interface between the adsorbent phase and catalyst phase, which coexist in the material [2].The proper selection of adsorbents increases the thorough dispersion of the catalyst, surface area, pore volume and low acidity, which are prime parameters for pollutant removal. For this purpose, ZSM-5 zeolite with hetero atoms was proven to facilitate both catalysis and adsorption [3][4][5][6]. A number of science workers studied the transition metal ZSM-5 considering their role as catalysts [7,[8][9][10].…”

Decomposição do NO sobre Cu suportado em zeólitas

“…Da literatura obtemos que diversos experimentos de RTP de catalisadores de Cu suportado mostram que a redução do cobre pode ocorrer em dois estágios, apresentando dois picos de redução. Segundo alguns autores [20][21][22] …”