FTIR Study of CO Adsorption on Ni−ZSM-5

Abstract

Adsorption of CO on Ni-ZSM-5 reveals the existence of two kinds of Ni 2+ ions, with the respective stretching frequencies being at 2220 and 2212 cm -1 . The carbonyl complexes are resistant to evacuation at room temperature, which is explained by the high electrophilicity of cations in a ZSM matrix. At 85 K and in the presence of CO, part of the Ni 2+ -CO species are converted into Ni 2+ (CO) 2 dicarbonyls (2204 cm -1 ) which are characterized by a very low stability and easily lose one of their CO ligands. Interaction of Ni-ZSM-5 with CO at 673-773 K results in a preferential reduction of the Ni 2+ ions which form the carbonyls characterized by the band at 2220 cm -1 . CO adsorption at room temperature on the reduced sample leads to the formation of Ni + (CO) 2 gem dicarbonyls (ν s at 2136 cm -1 and ν as at 2092 cm -1 ) which are converted, during evacuation, to linear Ni + -CO species (2109 cm -1 ). The dicarbonyl structure is proved by 12 CO-13 CO coadsorption, and the mixed Ni + ( 12 CO)( 13 CO) species are characterized by ν( 12 CO) at 2123 cm -1 and ν( 13 CO) at 2058 cm -1 . At low temperature, a third CO molecule is coordinated to the Ni + cations, thus producing tricarbonyls (2156, 2124, and 2109 cm -1 ). The latter species lose one of their CO ligands during evacuation at 85 K and are converted back into dicarbonyls. The Ni + sites are easily oxidized in the presence of O 2 . However, the Ni 2+ ions produced differ in properties from the initially deposited cations and are easily reduced to Ni + even at ambient temperature.

A DFT Study of CO Catalytic Oxidation by N2O or O2 on the Co3O4(110) Surface

“…These analyses revealed that there are two types of interactions for CO adsorption at Co oct and O 2f sites, namely s-donation and p*-back-donation, and the latter is responsible for the observed red-shift. The CO red-shift and the same bonding mechanism have been reported in a number of theoretical (CO/CuCr 2 O 4 (100), [42] CO/Cu 2 O(111), [43,44] CO/Al 2 O 3 [45] ) and experimental (CO/Co 3 O 4, [39] CO/Ni-ZSM-5 [46,47] ) studies. On the Co 3 O 4 (110)-B defect surface with an O 2f vacancy, CO adsorbs at the O 2f -vac site through carbon.…”

Importance of Size and Distribution of Ni Nanoparticles for the Hydrodeoxygenation of Microalgae Oil

“…This led to the presence of cationic Ni. The bands at 2210-2212 cm À1 are assigned to Ni 2 + À CO, [24][25][26][27] whereas the two bands at 2136-2137 and 2092-2094 cm À1 are ascribed to the symmetric and asymmetric CO stretching of geminal Ni + (CO) 2 dicarbonyls. [21,22,28,29] The Ni + ion is speculated to originate from the reduction of Ni 2 + in the reducing environment of CO. [30] The fact that two CO molecules are attached to one Ni + cation compared with Ni 2 + À CO can be rationalized by the higher ionic radius of Ni + .…”

New bifunctional Ni–H-Beta catalysts for the heterogeneous oligomerization of ethylene

“…For instance, in a precedent work Yashima et al [16] [19,20,21,22,24], reduction with H 2 [22] or CO at high temperatures (350-450ºC), [21,25,26], or even upon contact of the catalyst with ethylene [19,20]. It is pertinent to mention here that in most of the above studies the conclusion that monovalent Ni + species are the active sites relied on room temperature CO-FTIR characterization results [12,19,20,21,24].…”