ADSORBATE—ADSORBENT INTERACTIONS IN THE CHEMISORPTION OF CARBON MONOXIDE¹

Copper Sites in Cu-ZSM-5 Zeolites. Part II. An Identification of Defective AlOCu+ Sites by FTIR

“…High-frequency CO (>2170 cm -1 ) is generally related to those transition metal ions with high oxidation states (>2). These metal ions such as Zn 2+ , Ni 2+ , and Cu 2+ are of small ionic size and high electron affinity and thus interact with CO through weak π back-donation coupled with σ bonding, which would result in high C−O frequencies. ,, In an early paper about the CO adsorption on CuO, the 2173 cm -1 band was assigned to the CO vibration at Cu 2+ site and the number of valence electrons of the adsorbed CO molecule was estimated, based on an empirical formula, to be 9.35 as compared with 10 for gaseous CO (2143 cm -1 ), 9.76 for the CO adsorbed at Cu + (2156 cm -1 ), and 9.0 for CO + (2183.9 cm -1 ). This indicates obviously a rather weak π-back-donation from Cu 2+ to CO, weaker than that from Cu + to CO. Conventionally CO is considered as a strong π-acceptor and the metal-to-CO π back-donation to be responsible for the thermal stability of many classical transition-metal carbonyl complexes .…”

“…At room temperature the CO adsorption on a dehydrated Cu-ZSM-5 sample was found to produce infrared absorption bands at 2176, 2156, and 2138 cm -1 . The carbonyl bands at 2176 and 2156 cm -1 were previously identified as the C−O stretching vibration over Cu 2+ and Cu + , i.e., Cu 2+ CO and (AlOSi)Cu + CO, respectively, ,− whereas the assignment of the 2138 cm -1 band is still controversial at present. To better understand the nature of the Cu site related to the carbonyl band at 2138 cm -1 , the CO adsorption on the dehydrated Cu-ZSM-5 sample is studied by in-situ IR measurement as a function of Ar purge and heating.…”

Two semiempirical equations which relate viscosity and the intradiffusion coefficients for multicomponent systems

“…By applying eq 43a of ref 2 and eq 2b and 6, eq 5 is reduced to the equation V S* aVm~MRT WZV) ¿=0 = aVm™RT (cí/TV) (7) ¿=*0 Here, >7 is the intradiffusion coefficient1•2 of component i; by definition Z),•7 is equal to the tracer-diffusion coefficient for component i when isotopic mass effects are neglected. Thus, according to this development the viscosity is to be approximately related to the reciprocals of the intradiffusion coefficients, with the units cm2 sec-1, of all the components in the system times their respective concentrations in mol/cc.…”

“…With regard to CO we recall the works of O'Neill and Yates2 and Peri8 on NiO, Pichat, et al,* on Th02, Taylor and Amberg6 on ZnO, and Gardner, et aZ., [6][7][8] on several metals and oxides.…”