INTAS project 1116-97

 Description of the project results

New generation of catalytically active solid acids based on organically functionalized silicas were obtained. Several directions for preparation of strong solid Brönsted acids were tested and next one were most extensively developed, as the most promising (in respect to their high acidity and stability):

1.      Covalent immobilization of alkylsulphonic acid (SiO₂-SO₃H) on silica surface. (Several synthetic strategies can be used to obtain most stable and uniformly modified silica with strong acidity.)

2.      Tungsten and molybdenum heteropolyphosphates bonded on alkylammonium and alkyl phosphonium silicas.

To improve the materials properties, namely acidity, hydrophobisity and catalytic activity next approaches were developed:

1.       To increase the catalysts total acidity, low-temperature fluorination of their surface based on treatment of modified material with anhydrous solution of ammonia fluorides was developed. With utilization of MAS ²⁹Si, ¹⁹F NMR, mass-spec controlled thermodesorption and DRIFT it was shown that two types of fluorinated silicon species: tetrahedral surface bound hydroxy-species with general formula O_nSi(OH)_4-n-mF_m, and octahedral one with formula [F_nSi(OH)_6-n]^2- are formed. The thermal treatment leads to the decomposition of octahedral complexes with the removal of fluorinated silicon species to the gas phase in the form of fluorides and hydroxyfluorides. Tetrahedral species O₃-SiF are formed from octahedral. Further heating causes Si-F migration with subsequent removal of residual fluorine as silicon fluorides from the surface up to its complete removal at 600°C.  Increasing of hydrophobisity for fluorinated silica has been demonstrated from the thermal dependency of water desorption from the material surface.

2.       The procedure for controlled introduction of Lewis acid centres on the carrier surface was developed. Bulky titanium and Zirconium alkoxydes were used for this. As a result new hybrid materials simultaneously containing Lewis (from 10 till 600 μmol/g) and Brönsted acid sides (from 30 to 300 μmol/g) were obtained.

Impact of the science in the field

• Developed procedure demonstrates its potential in creation of surface modified materials with given properties and namely for preparation of silica-based hydrophobic materials with covalently immobilized acids with both Brönsted and Lewis nature. Concentration of hydrophobic, Brönsted and Lewis sites can be controlled in wide range.
• New procedure for low-temperature fluorination of silica was developed and used to increase the material acidity and hydrophobisity.
• Site-reaction that has effect on composition of interfacial layer was discovered.

Impact on technology and commercial exploitation

The project solid acids demonstrated high catalytic activity in reaction of ethyl-tret-butyl ester (ETBE) synthesis that widely used as antidumping additive to the car petrol to increase octane number. Their specific catalytic activity were in about 100 times higher then  industrial one (Amberlyst-15^®). Project catalyst selectivity for ETBE formation is also higher (up to 95%) then for industrial catalysts (80% for Amberlyst-15). With respect to proposed materials high thermal stability and better kinetic characteristic, developed in the project silica based acids can replace existing catalysts in commercial process of ETBE synthesis.   

It is also important that Ukraine has no sources for preparation of catalysts using in ETBE synthesis and has to import it. Introduction of the developed composites to industry decrease the product price. Application for patent from Ukraine will be made.