The Development And Application Of Industrial Catalyst Coating Binder

With the rapid development of China's economy,the total emission of industrial NO_x has increased rapidly.This leads to 'the increasingly strict standard for NO_x emission,making the application and popularization of effective denitrification technology imperative.Selective catalytic reduction?SCR?of NO_x with NH₃ as a reductant has been widely utilized in industry.The main catalyst used in the SCR is composed of V₂O₅-WO₃/TiO₂,the powders of which are usually extruded into monolithic honeycomb for industrial application.However,such an extrusion could affect the mechanical strength.Moreover,it needs to consume large amounts of catalyst powders,making the process less cost-effective.Cordierite honeycomb ceramics have the advantages of high mechanical strength and low thermal expansion coefficient,which are promising matrix materials of monolithic catalysts.In this thesis,commercial V₂O₅-WO₃/TiO₂ powders were coated onto the cordierite and applied for NH₃-SCR denitration.It is expected that the work conducted herein could provide an economical path for the fabrication of monolithic SCR catalysts for industry.The key part for monolithic honeycomb catalyst fabrication is the powder coating.This process involves the use of a mixture of binder,catalyst powder and water.The bond strength of coating determines the mechanical strength and the catalytic performance of monolithic catalysts.At present,the binder used is mostly imported and thereby expensive.To solve this problem,the thesis first attempts to develop a binder with an independent intellectual property right,in order to replace the imported one and reduce the production cost for coated industrial molding catalyst.Adapting from related literature,single factor experiments were conducted to optimize the grouping of binder and auxiliaries for efficient binder formulation.The obtained formula was composed of base glue,crosslinker,chain extender,solvent and various auxiliaries.Among them,the silica composed of amorphous silica particles and water was selected as base glue due to its excellent bonding function.However,the pure silica glue was unstable and lack of surface functional group.As such,silane coupling agent I was introduced as a crosslinking agent to increase the surface functional groups.To further enhance the surface reaction with silica sol,silane coupling agent II acting as chain extender was also added.For additives,the ether solvent was selected to accelerate the reaction between silane coupling agent and silica sol due to its coexistence of lipophilic and hydrophilic groups.Titanate coupling agent was introduced to improve the amounts of fillers for enhancing the binding strength of the inorganic materials.Plasticizers were added to improve the toughness and hardness of curing layer and boron compounds were introduced to further improve the adhesive bond strength.By mixing the binder with commercial V₂O₅-WO₃/TiO₂ catalyst powders,industrial cordierite honeycomb catalysts were obtained.After subjected to BET,SEM,the effects of slurry properties?including the amount of binder and solid content?and processing parameters?including slurry coating path,coating time,the times of coating and baking temperatures?on the loading,bond strength and catalytic activity of monolithic honeycomb catalyst were explored.It was noted that the varied binder amounts could affect the coating efficiency and catalytic performance of the monolithic catalyst.Too much binder would inhibit the catalytic activity and too little would reduce the coating efficiency,both of which were not conducive to catalytic performance.The coating efficiency and catalytic activity were best with the viscosity of the powder at 1:5.The increase in slurry solid content would lead to the increase of coating load and catalytic activity,but the bond strength would decrease.The best solid content was found to be 40%.Ultrasonic extraction was better than conventional dip coating.The lengthening of coating time would destroy the adhesive structure,thereby reducing the bonding strength and lowering catalytic activity,whilst less time would not meet the minimum loading requirement.The coating time was best at 0.5 h.A single coating could meet the application requirements of coating efficiency and catalytic activity for the monolithic catalyst.After calcination at 350 ?,the catalyst could yield 98%DeNO_x efficiency under the condition of NO = 600 ppm,NH₃=600 ppm,O₂ = 4%and maintain stability.