When comparing catalytic performance of K Au TiO

For deriving insights into overall reaction pathways leading from CO2 to propanol, we performed catalytic tests at different contact times to achieve different degrees of CO2 conversion; the longer the contact time, the higher the conversion is. Fig. 6 shows the selectivity-conversion plots for all Cs–Au/TiO2 catalysts. In general, CO selectivity decreases with rising CO2 conversion, while propanol selectivity increases. The selectivity to propanal TAK-715 always below 5% and decreases with CO2 conversion. Similar selectivity-conversion profiles were previously reported by us for K-Au/TiO2 catalysts [14]. From a mechanistic viewpoint, such effect of CO2 conversion on products selectivity can be explained as follows. CO2 is primarily converted to CO through the RWGS reaction. Such in situ formed CO is inserted into C2H4 to yield propanal, which is further hydrogenated to propanol. Since the overall reaction scheme is valid for all catalysts irrespective of Cs loading, we put forward that the loading influences the kinetics of individual reaction pathways and thus determines the distinct catalyst selectivity in Fig. 5. The below discussion is aimed at elucidating possible origins of the promoter effect on catalytic performance.