Influence of the preparation method, outgassing treatment, and adsorption of NO and/or O{sub 2} on the Cu{sup 2+} species in Cu-ZSM-5: An EPR study

Journal Article · Fri Mar 10 04:00:00 EST 2000 · Journal of Catalysis

DOI:https://doi.org/10.1006/jcat.1999.2750· OSTI ID:20020867

Soria, J; Martinez-Arias, A; Martinez-Chaparro, A; Conesa, J C; Schay, Z

Two Cu{sup 2+}-loaded ZSM-5 zeolites prepared by ion exchange from liquid solution (LS) and solid-state reaction (SR) are studied by EPR after vacuum treatments at several temperatures, T{sub v}, up to 413 K and subsequent NO and/or O{sub 2} adsorption. In addition to the changes in Cu{sup 2+} coordination upon dehydration, from octahedral to square pyramidal and planar, outgassing produced in sample LS a decrease of the Cu{sup 2+} EPR signal, initiated by brief outgassing at 298 K and reaching a maximum (ca. 75% of the total copper not detected) for T{sub v} = 383 K. This is ascribed to fast spin relaxation, due either to a ligand geometry effect or to the establishment of copper-copper interactions. Subsequent NO adsorption at 298 K generated (Cu-NO){sup +} complexes, apparently by reaction of square planar Cu{sup 2+} (possibly assisted by water or OH{sup {minus}} still present), while NO and O{sub 2} coadsorption led to a large change, all copper now being EPR-visible either as a sharp signal for a square planar species or as a broad band due to spin-interacting Cu{sup 2+}. For sample SR, the resolved Cu{sup 2+} EPR signals, representing ca. 25% of the total copper, behave similarly to those found in sample LS (except that their overall intensity decreases little upon outgassing), but most copper exists as Cu-oxide clusters giving a broad EPR signal. The latter, resulting from the solid-state preparation method, seem scarcely reactive on adsorption of NO or NO + O{sub 2}; they may be connected with the lower catalytic activity in NO decomposition previously observed for this latter sample.

• Research Organization: CSIC, Madrid (ES)
• OSTI ID: 20020867
• Journal Information: Journal of Catalysis, Journal Name: Journal of Catalysis Journal Issue: 2 Vol. 190; ISSN 0021-9517; ISSN JCTLA5
• Country of Publication: United States
• Language: English

Related Subjects

01 COAL, LIGNITE, AND PEAT
54 ENVIRONMENTAL SCIENCES
ADSORPTION
AIR POLLUTION CONTROL
CHEMICAL PREPARATION
COPPER
DECOMPOSITION
DEGASSING
NITRIC OXIDE
SORPTIVE PROPERTIES
ZEOLITES