Green Synthesis Of MFI Zeolite And Its Catalytic Performance

MFI zeolites such as TS-1 and ZSM-5 are widely used in the catalytic industry,due to their excellent ion exchange capacity,hydrothermal stability,and shape selectivity.Hydrothermal methods are the most commonly used process for synthesis of zeolites,an energy-consuming process that often uses organic substrates.Which is harmful to the environment,and contradicts the concepts of green chemistry and sustainable development.At present,green synthesis of zeolites can be achieved through green raw materials,green synthesis conditions,and green synthesis routes.Many potential silica sources are rich in the natural biomass and solid wastes such as rice husk ash,distiller’s grains ash,and industrial silica gel waste.However,recovering the silica sources usually requires a complex pretreatment.Solvent-free synthesis of zeolites is considered a green synthesis method,which is no addition of solvents,no effluent,a single kettle with high yield,and a short crystallization period.In our work,MFI zeolites are synthesized using a solvent-free method from industrial silica-gel waste,rice husk ash,distiller’s grains ash.Moreover,investigate the modulation of active Ti species and in situ encapsulation of nickel in the TS-1 sample.Main findings are as follows:（1）MFI zeolites were synthesized with a high crystallization degree via a controlled ratio of the starting raw solids by a solvent-free method using silica-gel waste,rice husk ash,and distiller’s grains ash.The final ZSM-5 zeolite prepared from rice husk ash and distiller’s grains ash possess mesopores structure,which facilitate the mass transfer and diffusion efficiency of the reactant.In addition,TS-1 zeolites with a high crystallization were synthesized by means of silica gel waste.The prepared TS-1 samples possess typical hexagonal prismatic morphology,abundant framework titanium species,and without of anatase Ti O₂.Noteworthy,TS-1 sample synthesized from acid silica gel exhibited comparable well morphology and degree of crystallization to the TS-1 sample prepared from commercial silica.In this work,industrial silica waste was used in TS-1samples without any pre-treatment.（2）Silica wastes with different acid or basic surface properties are directly used for solvent-free synthesis of TS-1 zeolites.The states of Ti species,Si/Ti molar ratios(n _Si/n _Ti),and morphology of final TS-1zeolites can be controlled by the pristine surface properties and additional（NH₄）₂CO₃.When n _Si/n _Ti=100,the results show that TS-1samples synthesized from acid silica wastes exhibit more framework Ti species.As the titanium content increases to n _Si/n _Ti=50,high coordination Ti O₆ active species are shown in TS-1 samples,and TS-1 samples formed from acid silica waste exhibit abundant Ti O₆ species than basic wastes.In addition,TS-1 samples have elongated c-axis lengths with increasing Ti content.At n _Si/n _Ti=30,TS-1 sample synthesized from acid silica waste possesses an abundance of Ti O₆ species.And the conversion of chloropropene reaches 66.7%,with a selectivity of more than 98.5%for epichlorohydrin.（3）Metal Ni-loaded TS-1 zeolites were in situ prepared from different metal precursors（Ni-EDA,Ni-TAPTS）via a solvent-free methods.And the metal precursors are complexes formed from organic ligands ethylenediamine（EDA）,3-[2-（2-aminoethylamino）ethylamino]propyltrimethoxysilane（TAPTS）and Ni ions,respectively.The investigations show that Ni was highly dispersed in TS-1 zeolite when the Ni-EDA complex was used as the metal precursor,and that Ni was mainly present as divalent Ni O.Additionally,TS-1 zeolite prepared at Ni=2 wt%and n _Si/n _Ti=60 had a much higher penetration sulphur capacity in carbonyl sulphur adsorption（0.80 mg S/g）than the TS-1 sample without metal Ni loading（0.42 mg S/g）.However,when using Ni-TAPTS as metal precursor,excessive precursor（Ni>2 wt%）will disrupts the synthesis environment of TS-1 zeolite,resulting in an amorphous state.Notably,at lower Ni loadings（Ni<1 wt%）,the TS-1 zeolite prepared from Ni-TAPTS also has a high penetration sulphur capacity（>0.56 mg S/g）.