Boreskov Institute of Catalysis of the Siberian Branch of Russian ...

PP-III-11LOW TEMPERATURE OXIDATION OF CARBON MONOXIDEON POTASSIUM PROMOTED GOLD DISPERSEDON Fe 2 O 3 , TiO 2 , Al 2 O 3 SUPPORTSWojciech K. JóźwiakTechnical University of Lodz, Institute of General and Ecological Chemistry, 90-924 Lodz,ul. Żwirki 36, Poland, fax: 048-042-631-31-28, e-mail: wjozwiak@p.lodz.plDespite the intensive efforts the nature of gold catalyst active sites and the mechanism oflow temperature carbon monoxide oxidation CO + O 2 → CO 2 remains unresolved and themode of oxygen activation is one of the least understood reaction step. In this work the role ofpotassium ions deposited on Au/support (Fe 2 O 3 , TiO 2 , Al 2 O 3 ) catalysts was investigated.Supported catalysts 0.5 – 10% Au/support (Fe 2 O 3 , TiO 2 , Al 2 O 3 ) were prepared by twomethods: conventional impregnation and deposition precipitation. In the case of impregnationmethod commercial supports were impregnated in aqueous solution of HAuCl 4 (pH ≈ 2).After water evaporation catalyst samples were dried at 60 °C in air. A fraction of sampleswere additionally impregnated with aqueous solution of KOH (pH > 13) and finally catalystswere dried at 60 °C. In deposition precipitation method aqueous solution of Na 2 CO 3 was usedas precipitation agent for HAuCl 4 solution to achieve pH value in the range 7 – 8 and thenappropriate amount of commercial support was admixed and the obtained catalysts were driedat 60 °C in air. The physicochemical properties of supported catalysts were investigated by:low temperature nitrogen adsorption – BET(N 2 ), temperature programmed reduction – TPRH 2 and diffraction method – XRD, second ions mass spectrometry – ToF-SIMS and electronspin resonance spectroscopy – ESR. The catalysts were tested in CO oxidation reaction usinga fixed bed quartz reactor. Typically, CO (3% in He) and O 2 (6% in He) were mixed and fedto the reactor at controlled flow rate (usually 50 cm 3 /min) through the catalyst sample (0,20 g)in appropriate temperature range, and the products were analysed at every 50 °C temperatureinterval, using on-line gas chromatography. The applied molar ratio O 2 : CO being about 4 : 1reflects the oxidative conditions commonly experienced in industrial practice of carbonmonoxide removal.Acid-base character of Au/support catalyst surface can play important role in catalyticperformance. Different acidity in preparation procedure: impregnation (pH = 2) in comparisonwith precipitation-deposition (pH = 7 – 8), and KOH addition (pH > 13) results in thehydrolysis of chlorine ions and their re-adsorption taking place on support surface:[AuCl 4 ] – + 4 OH – → [Au(OH) 4 ] – + 4 Cl – .323