Study On Novel Approaches To The Synthesis Of Au/TS-1 Catalysts For Gas-phase Propylene Epoxidation In The Presence Of O₂ And H₂

Catalysis is one front on which scientists and engineers are making a great contribution in making the production and manufacture of consumer goods both more cost effective and environmentally friendly.By developing highly specific and active catalysts,fewer undesirable byproducts will be produced thereby saving energy that would be expended in costly separation processes.In line with these efforts,high performance gold on titanium silicalite-1(Au/TS-1) catalysts for direct gas-phase propylene epoxidation using O₂ as the oxidant in the presence of H₂ were synthesized using a novel approach that uses gold(â… ) thiosulfate complex as a precursor.Both bioreduction-assisted synthesis and chemical synthesis approaches were explored in this research.One-factor-at-a-time experimental design was implemented to investigate variables that influence the performance of the synthesized catalysts,namely:gold loading,Na₂S₂O₃:Au mole ratio,pH,kind of acid for pH adjustment,and post-calcination temperature.Characterization techniques such us X-ray diffraction measurements,transmission electron microscopy,UV-Visible diffuse reflectance spectroscopy and scanning electron microscopy were used to elucidate the structure and properties of the catalysts produced and confirmed the deposition of gold nanoparticles on TS-1 support.Gas chromatographs equipped with thermal conductivity detectors(TCD) and a flame ionization detector(FID) were used to analyze the composition of effluent gases from the glass tubular flow reactor during catalyst tests.A catalyst prepared under the following conditions:1.93%nominal Au loading, Na₂S₂O₃:Au ratio of 4.30,pH 2 adjusted with HCl,and post-calcinated at 573 K, exhibited remarkable performance.With it,11.2%propylene conversion was attained and 63.3%PO selectivity registered at a space velocity of 4000 ml g^-1_cat h^-1 during catalyst tests in a 10 mm×100 mm glass tubular flow reactor.This performance is equivalent to 7.1%PO yield which is comparable to one of the best reported PO yields (8.4%) registered by Au/TS-1 catalysts tested under similar conditions.This study provides an opening for further elucidation of a very promising Au/TS-1 catalyst preparation method which will go a long way in making production of polyether polyols,propylene glycols and propylene glycol ethers more environmentally friendly and sustainable.