Rong Zhang

In situ FTIR studies of methanol adsorption and dehydrogenation over Cu/SiO2 catalyst

Abstract In situ FTIR spectroscopy was used to identify the adsorbed species and the intermediates during methanol dehydrogenation over Cu/SiO2 catalyst, and a schematic reaction network was proposed. Methoxy species on copper, which were derived from adsorbed methanol, dehydrogenated into formaldehyde. Then several competitive pathways took place. The adsorbed formaldehyde could desorb to the gas phase, or react with another adsorbed methoxy group to form methyl formate, and/or undergo further dehydrogenation to CO and H2. Carbon monoxide formed from the decomposition first adsorbed on high-index planes of copper, and then on low-index planes as the reaction progressed. With the increase of temperature, the concentration of formaldehyde and CO in gas phase increased, and that of methyl formate decreased.

Strong metal–support interactions between Ni and ZnO particles and their effect on the methanation performance of Ni/ZnO

A Ni/ZnO system was prepared by coprecipitation and characterized after reduction at different temperatures (350, 400, 450 and 500 °C) using TG-MS, H2-TPR, N2 physisorption, XRD, SEM, H2 and CO chemisorption, TEM, EPR and XPS. H2 and CO chemisorption experiments combined with XRD, SEM and TEM analyses showed evidence for strong metal–support interactions (SMSI) between Ni and ZnO particles, and the degree of SMSI strengthened as the reduction temperature rose. TEM, EPR and XPS studies revealed that the generation of SMSI was attributed to the geometric decoration of Ni particles by ZnO and electron transfer from ZnO to Ni atoms as well as the chemical interaction between Ni and ZnO leading to the formation of a NiZn alloy. Methanation of CO was used as a probe reaction to characterize the effect of SMSI on the catalytic performance of Ni/ZnO. The results showed that SMSI in general had a remarkable suppression effect on the methanation activity, but a light-degree SMSI state facilitated enhancement of the selectivity and stability of CO methanation. Interestingly, the suppressed activity can also be restored with different degrees via re-oxidization and re-reduction treatments under mild conditions. The discovery of SMSI between Ni and ZnO gives a new understanding of the interaction between Ni and supports, and provides a way to tune the interaction between Ni and supports as well as a way to regulate the methanation performance of the Ni/ZnO catalyst or Ni-based catalysts.

Gas mixing in a multi-stage conversion fluidized bed (MFB) with secondary air injection. Part I: an experimental study

This paper investigated the distribution of secondary air after injection into a multi-stage conversion fluidized bed (MFB) cold model. Carbon dioxide (CO2) was used as the tracer and its concentration was tested. The effects of the velocity of the primary air and secondary air, the particle circulating rate, and the diameter, number and included angle with the central line of the riser of injectors on the distribution of CO2 were studied. Single- and multi-injector systems were applied, in which different designs of the secondary-air injectors were used. The radial gas dispersion coefficient was calculated by the dispersed plug flow model (DPFM). The concentration profile of the tracer and calculated radial gas dispersion coefficients indicated that lower velocity of primary air, higher velocity of secondary air and particle circulating rate, bigger size of injectors and smaller included angles of injectors helped the gas mixing of the secondary air in the MFB. The tangential injection of secondary air would induce a gathering of gasification agents in the region near the wall, which was undesirable for the operation of the MFB gasifier. The variation of the penetration depth of the secondary air indicated that the penetration depth under multi-injector system was smaller than that under single-injector system when other operational parameters were uniform. Thus, according to numbers of injectors, taking the included angles between injectors and the central line of the riser into consideration, the penetration depth of the secondary air was correlated with operational parameters.