Preparation Of Titanium-based Electrocatalytic Membranes And Research On Their Catalytic Electrochemical Reduction Reaction

Lignin derivatives are naturally occurring renewable raw materials,and high value-added chemicals such as aromatic alcohols and phenols can be prepared by catalytic hydrodeoxygenation.At present,biomass conversion still faces many problems,such as the need for high temperature and high pressure,expensive catalysts,etc.,which seriously hinder its large-scale application.Therefore,it is of great scientific and application significance to develop strategies for selective hydrodeoxygenation under mild conditions,among which electrocatalytic hydrogenation technology has broad application prospects as a clean,safe and efficient catalytic method.In this paper,based on sulfide-supported titanium membrane electrodes（Ti S₂NRs/Ti）,electrocatalytic membrane reactor（ECMR）was constructed to realize the hydrodeoxygenation reaction of lignin model compound-vanillin under mild conditions.Hydrogen reduction and transformation of lignin provide new research ideas.Its main research contents are as follows:（1）The Ti S₂NRs/Ti electrocatalytic membrane electrodes consisted of the one-dimensional Ti S₂nanorods（NRs）and Ti membrane were successfully prepared by a one-step hydrothermal method using sodium sulfide as the sulfur source Compared with the substrate titanium film,the redox peak potential difference（ΔE_p）of Ti S₂NRs/Ti film electrode decreases,the peak current response value increases,the interface resistance decreases,and the electrochemical energy is significantly improved.The reason is that one-dimensional sulphide nanostructure is conducive to electron transfer and electrolyte mass transfer.（2）Using tubular Ti S₂NRs/Ti electrocatalytic membrane as cathode,titanium sheet as anode and Na₂SO₄ as electrolyte,the H-type cell electrocatalytic membrane reactor（H-ECMR）was constructed for nitrobenzene reduction.CV tests show that the reduction peak current increases obviously with the addition of nitrobenzene,which means that nitrobenzene is successfully reduced at the cathode.When the initial concentration of nitrobenzene is 30.0 mmol L^-1,the current density is 1.0 m A cm^-2 and the residence time is 25 min,the conversion of nitrobenzene is more than 99%and the selectivity of aniline is 100%.（3）The electrocatalytic reduction of vanillin was carried out by using tubular Ti S₂NRs/Ti electrocatalytic membrane as cathode.Through the design of the reactor and the optimization of reaction parameters,two products of vanillin and 4-methyl guaiacol could be obtained,and the conversion and product selectivity of vanillin could be adjusted.When the initial concentration of vanillin is 30.0 mmol L^-1,the current density is 2.5 m A cm^-2 and the residence time is 25 min,the conversion of vanillin in single cell ECMR is 59.42%,and the selectivity of vanillin is the highest,which is 79.67%.In H-ECMR,the conversion of vanillin was 76.9%,the selectivity of vanillyl alcohol was61.2%,while the selectivity of 4-methyl guaiacol increased to 6.27%,because H-ECMR was beneficial to the further hydrogenation of vanillin.Through the study of the kinetics and mechanism of the reaction,it is proved that the reaction is a series reaction,and the product vanillin can be further hydrogenated to 4-methyl guaiacol,in which the production of reductive free radical active hydrogen（H^*）by water electrolysis is the key to the rapid hydrogenation and deoxidization of vanillin.