Characterization of sulfided molybdenum/alumina catalysts by temperature-programmed reduction and low-temperature Fourier transform infrared spectroscopy of adsorbed carbon monoxide

On the surface sites of MoP/SiO2 catalyst under sulfiding conditions: IR spectroscopy and catalytic reactivity studies

“…The band at 2045 cm −1 shifts to higher frequencies when the treatment temperature is increased, e.g., to 2047 cm −1 at 373 K, to 2049 cm −1 at 473 K, to 2055 cm −1 with a shoulder at 2090 cm −1 at 573 K, and to 2100 cm −1 at 673 K. Meanwhile, a shoulder at ca. 2055 cm −1 can still be distinguished for the sample treated at 673 K. The appearance of the band at 2100 cm −1 indicates the sulfidation of the phosphide surface because this is a characteristic band of CO adsorbed on sulfided Mo catalyst and has been assigned to linearly adsorbed CO on cus Mo 2+ sites [21,23,27]. The results show that the surface of the MoP/SiO 2 catalyst is partially sulfided when treated with the thiophene/H 2 mixture at 673 K. A separate detection of the changes of thiophene itself during the treatments at different temperatures shows that thiophene becomes reactive with hydrogen on the MoP/SiO 2 catalyst at and above 373 K. Thus, the gradual sulfidation of MoP/SiO 2 catalysts can be ascribed to the HDS of thiophene [31][32][33][34].…”

“…According to the preparation process, the passivated MoP/SiO 2 sample reduced at 923 K can be regarded as fresh molybdenum phosphide on silica. Therefore, adsorbed CO on fresh MoP/SiO 2 exhibits a characteristic band at 2045 cm −1 that can be due to adsorbed CO on Mo sites [23][24][25][26][27][28][29] on the surface of MoP. The fresh sample is denoted as MoP/SiO 2 on which following experiments will be carried out.…”

Carbon Monoxide Adsorption on Molybdenum Phosphides: Fourier Transform Infrared Spectroscopic and Density Functional Theory Studies

“…Generally speaking, linear carbonyl species coordinated to Mo δ+ (3 < δ < 5) sites exhibit ν MoC-O frequencies higher than those of free CO molecules (2143 cm -1 ). 6,15,16,26,28 In contrast, those held by Mo δ+ (0 < δ < 3) sites exhibit ν MoC-O frequencies of <2143 cm -1 . 25 A band at 2070-2050 cm -1 can be assigned to adsorbed CO on Mo 2+ .…”

“…6,15,16,[25][26][27][28][29][30] These studies can be used as references for the assignment of the IR bands of adsorbed CO on MoP. Generally speaking, linear carbonyl species coordinated to Mo δ+ (3 < δ < 5) sites exhibit ν MoC-O frequencies higher than those of free CO molecules (2143 cm -1 ).…”

“…25 A band at 2070-2050 cm -1 can be assigned to adsorbed CO on Mo 2+ . 6,15,16,28,30 Therefore, the IR band at 2037 cm -1 can be safely assigned to the linearly adsorbed CO on the surface Mo atoms of the MoP/Al 2 O 3 catalyst, which may likely be positively charged, i.e., Mo δ+ (0 < δ < 2). To our knowledge, this is the first time an IR spectrum has been recorded for CO adsorbed on the surface sites of MoP.…”