abstracts - Институт катализа им. Г.К. Борескова

OP-II-8decrease in the activity is accompanied by the increase in the selectivity to crotyl alcohol.During the time of reaching the steady – state regime, the most active catalyst centers onwhich the hydrogenation of C=C bond prevails are subjected to partial poisoning, which leadsto the enhancement of C=O hydrogenation.Activity [μmols -1 g Pt-1]temp. red=120 O C temp. reaction=80 O C3505 wt.% Pt/α-GeO 23002wt. % Pt/α-GeO 22501wt. % Pt/α-GeO 22001500 50 100 150Time on stream [min]Selectivity to crotyl alcohol [%]temp. red=120 O C, temp. reaction=80 O C1005 wt. % Pt/α-GeO 22 wt. % Pt/α-GeO 2801 wt. % Pt/α-GeO 260402000 50 100 150Time on stream [min]Fig.1. (a) the changes of catalysts activity during the time on stream, (b) selectivity to crotylalcohol for catalysts containing different amount of platinumXRD patterns of the 5 wt. % Pt/α-GeO 2 catalyst reduced at 120, 200 and 300 o C revealedthat the reflex characteristic of metallic platinum Pt (2Θ=46,38) is observed only for samplereduced at 120 o C. TPR profiles of the catalysts show a significant consumption of hydrogen,starting from the temperature of 180-200 o C which is obviously connected with the α-GeO 2reduction. In lower temperatures ca. 120 o C K some surface reduction of the support occurs,leading to the creation of some Pt 0 – Ge δ+ sites on the surface, enhancing hydrogenation of theC=O bond. At higher reduction temperatures platinum can be converted into the inactive PtGespecies and/or totally covered by the partially reduced support. This could explain lack ofplatinum XRD reflexes for the catalyst reduced at the temperatures ≥ 200 o C, and the drop ofactivity for the samples reduced at the temperatures ≥ 170 o C. The mean particle size of5 wt. % Pt/α-GeO 2 catalyst determined from the broadening of Pt reflexes was about 11 nm,whereas the mean particle size distribution evaluated basing on TEM images 2 – 5 nm: 23 %,5 – 10 nm: 34 % 10 – 15 nm: 25 % and 15 – 20 nm: 16 % . Thus, mean crystallite sizesdetermined for 5 wt. % Pt/α-GeO 2 catalysts by means of XRD and TEM methods are in arelatively good accordance.198