Studies On Catalytic Steam Reforming Of Acetic Acid For Hydrogen

Catalytic steam reforming of bio-oil was one of the most promising hydrogen production approaches. Steam reforming of bio-oil over the nickel catalyst had more promising technology and economic use than the noble catalyst. However, carbon deposit which led to the rapid deactivation of catalyst was a fatal problem for the nickel catalyst. One of strategies which were employed to decrease carbon deposit on the catalyst aimed at modifying the surface catalyst via the addition of other alkali metals or transition metals. In this work, the effects of Ni content, calcination temperature, reaction temperature, weight hourly space velocity (WHSV), promoter (lithium or yttrium) on hydrogen production on Ni/γ-Al2O3 in steam reforming of acetic acid (model compound) were investigated in a tabular reactor. The fresh or spent catalysts were characterized by X-ray photoelectron spectroscopy, temperatured-programmed oxidation, temperatured-programmed reduction, differential thermal analysis, X-ray diffraction, transmission electron microscopy, etc. The results showed that at CNi=12wt%,Tcal= 1073K,Treac=873K, WHSV=3.0h-1,the Ni/γ-Al2O3 catalyst exhibited the best performances. The effects of Ni content, calcination temperature, promoters (lithium or yttrium) on carbon deposition were also investigated in this work. The results showed that two types of carbon species, carbide-like carbon and graphitic carbon with different thermal stability and reactivity were deposited on the catalyst, which were signicantly affected by Ni content, calcination temperature and promoters of lithium or yttrium. With the increasing of Ni content, carbide-like carbon decreased but graphitic carbon increased. The catalyst with higher calcination temperature promoted the transition of carbide-like carbon. The anti-carbon-deposition performance of the catalysts was improved remarkably by the addition of lithium, which promoted the gasification of carbide-like carbon and suspressed the deposition of graphitic carbon.The adsorption modes of C on the clean Ni(111) surface were investigated by DFT to study coke formation on the nickel catalyst in steam reforming of acetic acid. The adsorption energies, adsorption structures, charge density difference, local density of states (LDOS), and Mulliken population were calculated in the coverage range of 0.167-1.0ML. The results showed that the hcp and fcc hollow sites were energetically favorable for all the coverage range considered. The LDOS analysis suggested that the formation of adsorption bonding was mainly due to the hybridization between the C2p and Ni3d orbitals. The adsorption energy decreased with the increasing of the coverageθdue to the occupied anti-bonding states from C2p and Ni3d hybridization. The analysis of charge density difference and Mulliken population suggested that a net charge flow of electrons induced by the adsorption from the Ni surface to C atom decreased with the increasing of the coverageθ.