ChemInform Abstract: IR Characterization of Group VI (61) Metal Carbonyls Adsorbed onto γ‐Alumina

Effect of χ-alumina addition on H 2 S oxidation properties of pure and modified γ-alumina

“…According to published data [20,40,41], the absorption bands at 21402155 cm -1 are attributed to CO hydrogen-bonded to hydroxyl groups on the alumina surface. The bands at 22102240 and 21802200 cm -1 are assigned [38,[40][41][42][43][44][45] to surface LAS that are characterized as unsaturated aluminum cations (Al 3+ ) with tetrahedral coordination [41,43,45] at crystallographic defects [46] and with octahedral coordination [44,45] at the regular defects of low-index crystallite faces [45][46][47], respectively. Shifting of the 2143 cm -1 frequency to greater wavenumbers indicates an…”

“…increase in the heat of CO adsorption and the strength of the LAS [38,43,44]. Lewis acid sites are commonly classified as weak (21802205 cm -1 ), medium (22052220 cm -1 ), and strong (22202245 cm -1 ) according to the heat of CO adsorption [38,43].…”

“…Table 3 lists the Lewis and Brønsted acidities determined from the FTIR spectra of CO adsorbed on aluminas. The table shows that -Al2O3 and (+)-Al2O3 primarily contain weak LAS with a heat of adsorption equal to 3238 kJ/mol [38,44] and a CO stretching vibration at 21852197 cm -1 . Examination of FTIR data for samples containing -Al2O3 shows that the disordered -Al2O3 phase contributes significantly to the weak LAS content with a maximal concentration observed at 35% -phase.…”

“…-Al2O3, (+90%)-Al2O3, and -Al2O3 samples also have a small amount of intermediate strength LAS, which is confirmed by high frequency absorption bands at 2210, 2220, and 2212 cm -1 , respectively. Their heats of absorption are equal to 4249 kJ/mole [38,44]. Thus, aluminas with , +, and  crystal modifications differ significantly in their surface acidity.…”

“…-Al2O3 is known [45][46][47] to contain tetrahedrally coordinated Al 3+ at crystallographic de-fect sites as well as octahedrally coordinated Al 3+ ions at regular defects on low-index crystal faces. Based on FTIR data, these tetrahedral and octahedral Al 3+ configurations are LAS, which are characterized by high-(22102240 cm -1 ) and low-frequency (21802205 cm -1 ) bands, respectively, in the spectra of CO adsorbed on alumina [38,[40][41][42][43][44][45]. According to Table 3, tetrahedrally coordinated Al 3+ ions belong to -Al2O3, while octahedrally coordinated Al 3+ predominates in both -Al2O3 and samples modified with 1535 wt% -Al2O3.…”