Infrared Spectra of Carbon Monoxide and Carbon Dioxide Adsorbed on Chromia–alumina and on Alumina

Abstract

Infrared spectra of CO and CO:: adsorbed on chromia-alumina and on alumina surfaces have been determined. A band near 2200 cm-I formed by CO on both surfaces a t room temperature was due to a weak, non-activated sorption, but also contained a co~ltribution from a more strongly sorbed, activated species on the chro~nia-alurni~la. The assignment of this band was discussed in some detail. Bands in the region 1200-1800 c~n-' were co~lsiclered in terms of surface CO2-species, although in certain instances the appearance of bands a t 1750 and 1430 cm-' may have indicated carbonate ion formation.Followi~lg an infrared study of carbon ~llonoxide and carbon dioxide adsorbed on zinc oxide (1) investigations have now been extended to chromia-alumina and alumina catalysts. Previous studies of CO and COz adsorption using the infrared method with both metals and metal oxides include the well-ltnown work of Eischens and Plisltin (2, 3), correlations of vibration frequencies and number of valence electrons of CO surface species by Gardner and Petrucci (4, 5), and work on titania surfaces by Yates (6). EXPERIMENTALThe chromia-alumina catalyst was prepared by mixing chromium hydroxide and a l u n~i~l u~l l hydroxide gels which had been precipitated separately from solutiolls of the metal nitrates by ammonia. The mixed gel was then dried a t l l O o C for 24 hours and calcined a t 500' C in oxygen, resulting in a con~position of 41yo by weight of Crz03. The powder was compressed a t 40 to~ls/in? into a thin plate suitable for the infrared studies. The plate, which measured 1.3 cmX2.8 cmXO.1 mm, weighed about 100 ~n g and had a surface area of 108 m2/g. I t was mou~lted in a cell of 10-crn path length, si~nilar t o that described earlier (7). Cells of 5-mm path length were also used occasionally. Evacuation a t 300-400° C and 10-4-10-6 mm was carried out for 1-2 hours before gases were adsorbed. Spectra were then recorded on a Perkin-Elmer 21 spectrophotometer fitted with a sodillm chloride prism. The percentage transmission through the sample was 10-15yo a t 1800 cnl-I. The alumina catalyst was prepared in a manner analogous to that described for the mixed gels. RESULTSFigure l a shows the spectrum of the chromia-alumina sample, with a weak band appearing a t 1370 cm-' after heating for 1 hour in oxygen a t 320' C and outgassiilg a t rnln for 1 hour. Scattering by the sample of infrared radiation a t higher frequencies precluded ally study above 2500 cm-'.When the sample was allowed to stand in the cell a t room temperature for 24 hours a weak band appeared a t 1580 cm-I (Fig. lb). Then after further evacuation a t 350' C a broad intense band appeared a t 1530 cm-I with shoulders a t 1420 cm-I and a t about 1350 cm-I (Fig. lc). I t was only after first heating the sample in oxygen a t 300-350' C and then evacuating that the absorption in the 1300-1600 cm-I region was decreased to the level shown in Fig. la. This oxygen treatment led to an i~lte~lsification of the 1370 cm-' band.

Modelling the transient kinetics of heterogeneous catalysts. CO-oxidation over supported Cr and Cu

“…Hence, it can be concluded that CO is retained on the catalyst in two forms: one form is liberated as CO2 only when the catalyst is fully oxidized (100% 02, 1 h, 773 K), whereas the other type is already liberated as CO2 when the catalyst is partly reoxidized (2.5% 02, 240s, 533-613 K). Based on literature, the first type is addressed to a carbonate species and the second type to CO adsorbed on coordinatively unsaturated surface (cus) Cr 3+ sites (Little and Amberg, 1962;Shelef et al, 1968;Burwell et al, 1969;Zecchina et al, 1969;Bijsterbosch et al, 1992). Assuming that each chromium atom present at the catalyst surface is occupied by one CO after complete reduction, the total amount of retained CO gives the Cr dispersion of the catalyst, i.e_ 20%.…”

Adsorption of carbon dioxide by X zeolites exchanged with Ni2+ and Cr3+: isotherms and isosteric heat

“…This is probably due to the physisorbed state of CO 2 , commonly described by a linear complex, leading to adsorption by an extremity, i.e., an oxygen [26]. Such adsorption minimizes the adsorbateadsorbate interactions, contrary to the fundamental assumption of this model.…”

The use of metal–organic frameworks for CO purification

“…Further CO adsorption studies of mesoporous alumina have also focussed on CO removal, 65 while most studies have featured alumina for catalytic purposes. [66][67][68]…”