Preparation Of Molybdenum Oxide Composite Materials And Their Performances On Catalytic Oxidative Desulfurization

The combustion of fuels containing sulfides produces harmful SOx,which causes air pollution,damages ecological environment and endangers human health.Therefore,the development of low-sulfur even sulfur-free fuels has become inevitable,and the efficient and eco-friendly desulfurization technology is critical.Oxidative desulfurization(ODS)has attracted more attention due to its mild operating conditions,low cost and higher efficiency in the removal of thiophene sulfides.Because of its high catalytic efficiency and low cost,MoOx has good prospects in the ODS field.While the activity of ODS is limited duo to the poor dispersion of MoOx in the oil phase and few accessible active sites.The construction of composite catalysts and their catalytic system are considered as effective way to enhance the ODS activity.In this paper,three composite catalysts with porous hollow structures were developed to achieve uniform dispersion of MoOx active sites,generate more efficient active centers and enhance the activity of the active sites.The main research contents are summarized as follows:(1)A porous CoMoO4-Co3O4 hollow nanocage catalyst(CoMoO HNCs)was successfully obtained by self-template sacrificial method and calcination using ZIF67 as template and cobalt source.This strategy can effectively avoid the aggregation of MoOx and achieve high dispersion of MoOx active sites.The porous hollow structure and large specific surface area of CoMoO HNCs can increase the contact between active sites and reactants,and promote the mass transfer of ODS reaction.Meanwhile,the coordinated interaction of electrons between CoMo introduces more highly active oxygen vacancies,which contributes to enhance the catalytic activity.The CoMoO HNCs displayed excellent AODS activity and cycling stability:Using O2 as the oxidant,the catalytic dosage was only 5 mg,and the sulfur content of decahydronaphthalene simulated oil was 500 ppm,the CoMoO HNCs catalyst achieved 100%DBT removal for 1 h at 110℃ in 10 mL of simulated oil,and remained highly active after 10 cycles.This study uses air as oxidant,which is low cost,non-polluting,safe and efficient,laying a good basis for the industrial application of CoMoO catalysts.(2)The precursor of polydopamine-Mo(PDA-Mo)was prepared by the chelation of dopamine with molybdate in the water-in-oil liquid phase reaction,which was further treated with pyrolysis and oxidation to successfully obtain a MoOx/C hollow spheres catalyst.The limiting effect of the carbon prevents the excessive agglomeration of MoOx during pyrolysis and allows MoOx to be uniformly embedded in the carbon carrier.The partial oxidation of carbon on the surface can form more meso-/micro-pores and larger specific surface area(406.4 m2 g-1),and more oxygen vacancies,which increased the number of effective active sites and improved the catalytic efficiency.The structure-property relationship of the sample was investigated in the n-octane acetonitrile biphasic system.The MoOx/C-750-4 catalyst can achieve 100%desulfurization after 15 min when the extractant addition was 5 mL,n-octane simulated oil was 10 mL,sulfur content was 500 ppm,catalytic dosage was 5 mg,the molar ratio of H2O2/DBT was 4,and the reaction temperature was 60℃,and exhibited high activity after 10 cycles.(3)An amphiphilic Mo/HNT/S nanoreactor was successfully prepared by using halloysite nanotubes(HNT)as the carrier:By electrostatic deposition,MoOx was selectively introduced into the inner wall of the tube and tightly bonded with the Al2O3 layer;By surface grafting,hexyltrimethoxysilane was combined with the external surface silyl hydroxyl to increase the hydrophobicity.The hydrophobic outer surface of Mo/HNT/S catalyst enables it uniformly dispersed in simulated oil and increases the oil-water interface;While the hydrophilic inner cavity can effectively remain H2O2 and extract DBT,enhance the concentration of DBT in nanotube,and fully contact with the MoOx in the tube inner wall,thus the confinement effect of the nanotube can enhance the catalytic activity and cycling stability.The Mo/HNT/S nanoreactor showed excellent activity in the n-heptaneH2O2 system without extractant:Under the optimal reaction conditions,of m(catalyst)=40 mg,H2O2/DBT=4,V(model oil)=5 mL,S content=500 ppm,T=60℃,it took 15 min to completely remove DBT,the turnover rate can reach 67.5 h-1.When the reaction temperature was lowered to 25℃,the conversion of DBT achieved 100%for 3 h;and remained highly active after 5 cycles.Meanwhile,the oxidized product DBTO2 was selectively retained in the nanotubes,which can be removed from the oil phase together with the catalyst,and effectively combining the catalytic oxidation and oxidation product separation.This technology has opened up a new path for constructing low-cost,green and efficient catalytic materials.