Surface carbonyl species of copper supported on dealuminated Y zeolite

Abstract

Well defined surface carbonyls of Cu ^I with unusually narrow (ν _1/2 <5 cm ^-1 ) IR carbonyl bands are formed during the interaction of CO with copper supported on highly dealuminated Y zeolite. A Cu ^I monocarbonyl with an IR band at 2159 cm ^-1 forms, with additional CO, a dicarbonyl with well resolved IR bands at 2179 and 2153 cm ^-1 . Isotopic exchange experiments combined with corresponding force field calculations reveal the C _2v structure of the dicarbonyl and a correlation of the integrated carbonyl intensities shows the mutual conversion of mono- and di-carbonyl at the same Cu ^I site. The reversible equilibrium between the two species is dependent on both the temperature and the CO pressure, with a formation energy of the Cu ^I (CO) ₂ of 37 kJ mol ^-1 . The bond angle between the carbonyl groups in the dicarbonyl is estimated to be 113°. Using a controlled hydration, several aquacarbonyls could be observed dependent on the water content. An aquacarbonyl species with a carbonyl band at 2141 cm ^-1 is observed when the first doses of water are added. It is transformed, with more water, into species with IR bands at 2136, 2129 and, finally, 2123 cm ^-1 , which contain probably more than one water and/or hydroxy ligand coordinated to the Cu ^I .