Selective hydrogenation over earth-abundant metal catalysts is challenging but particularly valuable for practical applications in heterogeneous catalysis.Herein,we demonstrate that the catalytic selectivity of the commercial Raney nickel catalyst can be greatly tuned by modulation of the nickel surface by silica.Using quinoline hydrogenation as a model,we show that the silica-modified Raney nickel catalysts exhibit good activity,excellent selectivity,and long stability,whereas the undesired over-hydrogenation reactions are effectively hindered.In contrast,the pristine Raney nickel catalyst shows inferior selectivity for the targeted product.Mechanistic studies confirm a positive role of silica to facilitate the desorption of 1,2,3,4-tetrahydroquinoline from the catalyst surface,thus enhancing the product selectivity.
The catalytic hydrogenation of 2-nitro-4-acetylamino anisole(NMA)is a less-polluting and efficient method to produce 2-amino-4-acetamino anisole(AMA).However,the kinetics of catalytic hydrogenation of NMA to AMA remains obscure.In this work,the kinetic models including power-law model and Langmuir-Hinshelwood-Hougen-Watson(LHHW)model of NMA hydrogenation to AMA catalyzed by Raney nickel catalyst were investigated.All experiments were carried out under the elimination of mass transfer resistance within the temperature range of 70–100°C and the hydrogen pressure of 0.8–1.5 MPa.The reaction was found to follow 0.52-order kinetics with respect to the NMA concentration and 1.10-order kinetics in terms of hydrogen pressure.Based on the LHHW model,the dual-site dissociation adsorption of hydrogen was analyzed to be the rate determining step.The research of intrinsic kinetics of NMA to AMA provides the guidance for the reactor design and inspires the catalyst modification.
Transformation of lignin to valuable chemicals via sustainable pathways is recognized as one of the most efficient ways to explore its value and replace the nonrenewable petroleum resource. In this work, an environmental-friendly transfer hydrogenation process has been developed to convert lignin derived2,6-dimethoxybenzoquinone to 1,4-cyclohexanediol. Compared with previous work under hydrogen pressure(30 bar), this process uses isopropanol as both solvent and hydrogen donor, which significantly simply the operation process. The core of this study is the design and preparation of Mn modified Raney Ni catalysts by ball milling process. A series of Raney Ni Mn catalysts with different ball milling time and Mn content were prepared and investigated. Characterizations by X-ray diffraction(XRD), X-ray photoelectron spectroscopy(XPS), scanning electron microscope(SEM) and transmission electron microscope(TEM) etc. showed that Ni Mn Al alloy was formed during the ball milling process and then transformed to Ni Mn alloy after treatment by aqueous Na OH. After optimization, a yield as high as 86.1% could be achieved for 1,4-cyclohexanediol at 200℃ in only 1 h.
