Atmospheric Hydrodeoxygenation of Guaiacolover Nickel Phosphide Catalysts: Effect of Phosphorus Composition

摘要

The phosphorous composition of nickel phosphide catalysts in atmospheric guaiacol hydrodeoxygenation (HDO) was investigated. Various initial Ni/P molar ratios, ranging from 0 to oo, were used to prepare the catalysts. The physicochemical properties of the catalysts were characterized. The catalytic performances were evaluated in a continuous fixed-bed system at 300 °C with different contact times under atmospheric pressure. The phosphorous contents affected both the active phase compositions and catalytic performances of nickel phosphide catalysts. Ni2P, Ni_(12)P5, and M3P were identified as the major active phases on the Ni/P = 1, 2, and 3 samples, respectively. Mostly, the P-rich catalyst exhibited lower guaiacol conversions but higher amounts of deoxygenated products (e.g. benzene) and less coke than the P-lean sample did. A guaiacol HDO network containing demethylation (DME), demethoxylation (DMO), direct deoxygenation (DDO), hydrogenation (HYD), and transalkylation (TRA) was proposed. The intrinsic activity decreased following the order as Ni/P = 3 >1 >2 at short contact times, and Ni/P = 1 and 2 samples are likely to enhance the rate of hydrogen transfer at long contact times. The pseudo-first-order kinetics analysis also indicated that phosphorous content has a negative effect on guaiacol conversion. The product selectivity at zero guaiacol conversion revealed that the Ni/P = 1 sample promoted guaiacol DMO and phenol DDO. The samples with Ni/ P= 2 and 3 enhanced guaiacol DME and TRA. The bifunctional property (HYD on Ni and protonation on PO-H) of Ni2P/SiO2 and the Br0nsted acidity of Ni_(12)P5/ SiO2 and Ni3P/SiO2 affected their catalytic behaviors. Lifetime testings showed that all catalysts deactivated in long-term operations but with different extents. The Ni/ P = 1 sample displayed the highest deactivation rate of guaiacol conversion (~78 %) while the Ni/P = 3 sample had the lowest (~46 %). Coking and phosphide leaching are attributed to cause the deactivation of nickel phosphide catalysts in guaiacol HDO.