CO Adsorption on Hydrated Ru/Al₂O₃: Influence of Pretreatment

Abstract

The adsorption of CO on hydrated H2-, O2-, H2S-, and He-pretreated 5 wt % Ru/Al2O3 was investigated using attenuated total reflection IR spectroscopy (ATR-FTIR) to determine how the oxidation state of Ru influences CO-H2O interactions. The frequencies of the three IR bands (high frequency (HF), midfrequency (MF), and low frequency (LF)) that are observed when CO adsorbs on Ru/Al2O3 are influenced by (1) CO coverage (CO−CO interactions), (2) Ru oxidation state, (3) pretreatment gas, and (4) pretreatment time. Water red-shifts the CO features by as much as 116 cm−1and influences the MF/LF ratio in a complex mechanism involving both (1) blockage of CO adsorption on the LF site and (2) the formation of OH---CO interactions. While the LF band position is correlated to the adsorbate electronegativity and the MF band slightly correlates to CO coverage, the HF position is independent of either CO coverage or adsorbate electronegativity. These varying degrees of correlations can be rationalized using the extent of interaction between water and the adsorbed CO species by assuming the LF band is due to CO adsorption on an a-top site that is expected to have minimal interaction with coadsorbed water, while the MF and HF bands most likely arise from Ru(CO) m (OH) n (n, m ≥ 1) and Ru(CO) o (H2O) p (o, p ≥ 1), respectively.

Sacrificial Sucrose Strategy Achieved Enhancement of Ammonia Synthesis Activity over a Ceria-Supported Ru Catalyst

“…During H 2 chemisorption at 400 °C (Figure ), the H 2 uptakes are 1.37 and 1.96 equiv H 2 per mole of Ru for Ru/CeO 2 and SC-Ru/CeO 2 , respectively, demonstrating the higher hydrogen adsorption ability for the catalyst prepared by the sacrificial sucrose strategy. The hydrogen molecules can dissociate into H atoms on the Ru metal for the oxide-supported Ru catalyst, and then, the H atoms would react with the oxygen atoms of CeO 2 to produce hydroxyl groups. , These hydrogen species (H atoms or hydroxyl groups) might desorb from the catalysts by releasing H 2 molecule or water, , and the products are mainly dependent on the desorption temperature and the number of defect sites. , Water would undergo reversible dissociative chemisorption on CeO 2 , and thus it is impossible to fully remove all oxygen atoms related to water formation. It is found that the production of water may be related to the reactive hydrogen species and hydroxyls from the support, and thus, the metallic or the oxidized Ru species might function as transfer agents in the formation of the hydrogen molecule or water.…”

“…The hydrogen molecules can dissociate into H atoms on the Ru metal for the oxide-supported Ru catalyst, and then, the H atoms would react with the oxygen atoms of CeO 2 to produce hydroxyl groups. 36,52 These hydrogen species (H atoms or hydroxyl groups) might desorb from the catalysts by releasing H 2 molecule or water, 53,54 and the products are mainly dependent on the desorption temperature and the number of defect sites. 52,55 Water would undergo reversible dissociative chemisorption on CeO 2 , 52 and thus it is impossible to fully remove all oxygen atoms related to water formation.…”

Effects of Using Carbon-Coated Alumina as Support for Ba-Promoted Ru Catalyst in Ammonia Synthesis

“…The bands at 1356 and 1586 cm –1 are due to O–C–O stretching vibrations of formate associated with the support, − indicating the involvement of surface hydroxyl in converting CO into carbonate species. The peaks at 1985 and 2045 cm –1 are characteristic of multicarbonyl CO species on Ru 0 or partially oxidized Ru (Ru n + ). − Bands at approximately 2172 and 2118 cm –1 were assigned to gaseous carbon monoxide, , but in our study, these peaks can still be observed after the samples were purged with He (Figure ). We attribute the bands at approximately 2172 and 2118 cm –1 to adsorbed CO species.…”

Reaction Mechanisms and Rate Constants of Auto‐Catalytic Urethane Formation and Cleavage Reactions

“… We employ the DFT method B3LYP [41] with dispersion correction [60] (B3LYP‐D3) and TZVP basis set to optimize the geometry of reactants and transition states and to perform vibrational analysis. B3LYP is known to provide accurate geometries at comparably low computational cost [61,62] . Rotor scans are used to identify possible conformations of reactants and transition states.…”