The surface sites of supported molybdenum carbide catalyst derived from different synthesis stages have been studied by in situ FT-IR spectroscopy using CO as the probe molecule. Adsorbed CO on the reduced passivated Mo 2 C/Al 2 O 3 catalyst gives a main band at 2180 cm -1 , which can be assigned to linearly adsorbed CO on Mo 4+ sites. The IR results show that the surface of reduced passivated sample is dominated by molybdenum oxycarbide. However, a characteristic IR band at 2054 cm -1 was observed for the adsorbed CO on MoO 3 /Al 2 O 3 carburized with CH 4 /H 2 mixture at 1033 K (fresh Mo 2 C/Al 2 O 3 ), which can be assigned to linearly adsorbed CO on Mo δ+ (0 < δ < 2) sites of Mo 2 C/Al 2 O 3 . Unlike adsorbed CO on reduced passivated Mo 2 C/Al 2 O 3 catalyst, the IR spectra of adsorbed CO on fresh Mo 2 C/Al 2 O 3 shows similarity to that on some of the group VIII metals (such as Pt and Pd), suggesting that fresh carbide resembles noble metals. To study the stability of Mo 2 C catalyst during H 2 treatment and find proper conditions to remove the deposited carbon species, H 2 treatment of fresh Mo 2 C/Al 2 O 3 catalyst at different temperatures was conducted. Partial amounts of carbon atoms in Mo 2 C along with some surface-deposited carbon species can be removed by the H 2 treatment even at 450 K. Both the surface-deposited carbon species and carbon atoms in carbide can be extensively removed at temperatures above 873 K.

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An alumina-supported Mo2C catalyst is found to be as active as a conventionally used Ir/gamma-Al2O3 catalyst for catalytic decomposition of hydrazine tested in a monopropellant thruster.

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Adsorption and oxidation of chlorobenzene on Al2O3, TiO2-Al2O3, and MnOx/TiO2-Al2O3 have been studied by in situ Fourier transform infrared (FT-IR) spectroscopy. At room temperature, chlorobenzene is only physisorbed on Al 2O3, TiO2-Al2O3, and MnOx/TiO2-Al2O3, and gives the same IR spectrum as that for liquid-phase chlorobenzene. On Al2O3 no further interaction and reaction take place with treatment at higher temperatures (up to 773 K), while phenolates are observed for TiO2-Al2O3 and MnOx/TiO2-Al2O3 at 773 K. When the adsorbed chlorobenzene coexists with oxygen, formates are detected for Al2O3, while acetates are additionally observed for TiO2-Al2O3 above 573 K. For MnOx/TiO2-Al2O3, maleates are present at 573 and 673 K, while formates and acetates develop at 473 and 573 K. Almost all IR bands due to formates, acetates, and maleates disappear at 773 K, indicating that these oxygen-containing species are potential intermediates for the total oxidation of chlorobenzene.

The surface active sites of a fresh Mo 2 C/Al 2 O 3 catalyst and their evolution under passivation conditions were characterized by IR spectroscopy using CO as the probe molecule. It was found that adsorption properties of CO on the fresh sample were quite different from those of the reduced passivated one. Mo d1 (0 o d o 2) sites are mainly present on fresh Mo 2 C/Al 2 O 3 catalyst as probed by a characteristic IR band at 2054 cm À1 of adsorbed CO. When the fresh Mo 2 C/Al 2 O 3 catalyst in the IR cell is exposed to trace amounts of O 2 or H 2 O in situ at RT, the intensity of the 2075 cm À1 band declines. It shows that the fresh Mo 2 C/Al 2 O 3 catalyst can be oxidized by trace amounts of O 2 or H 2 O easily and the oxidation capacity of H 2 O is weaker than that of O 2 . IR spectra of adsorbed CO on a reduced Mo 2 C/Al 2 O 3 catalyst passivated by a 1% O 2 /N 2 mixture show that two weak bands at 2180 and 2095 cm À1 appear, which suggests that the passivation layer cannot be completely reduced, even by H 2 -reduction at high temperatures. For reduced Mo 2 C/Al 2 O 3 passivated by H 2 O or CO 2 , IR spectra of adsorbed CO give characteristic IR bands at 2081 and 2030 cm À1 , which indicates that the surface Mo atoms are in a state of Mo f1 (0 o f o 3). Thus, we found that the Mo 2 C/Al 2 O 3 passivated by H 2 O or CO 2 can be regenerated by H 2 treatment at 673 K and most of the active sites can be recovered. It is too active to control the passivation extent using O 2 as an oxidant, while Mo 2 C/Al 2 O 3 passivated by H 2 O or CO 2 can be regenerated by simple reduction with H 2 .