Construction Of MgAl Hydrotalcite-based Bifunctional Catalyst And Its Catalytic Study On Soot Combustion

Soot particles(PM)is one of the main pollutants in diesel vehicle exhaust,which seriously endangers the human environment and health.The development of high-performance catalyst is one of the effective means for PM elimination.In this thesis,the effects of preparation parameters on the physicochemical properties of calcined composite oxide(MAO)were investigated.Then,the noble metal Pd/Ag and alkali metal K were supported on the carrier to construct the Pd-K-MAO and Ag-K-MAO series bifunctional catalysts with the coexistence of basic sites and oxidation sites,which were used in soot catalytic combustion reactions.The effects of raw material ratio,precipitation environment and calcination temperature on the physicochemical properties of Mg-Al hydrotalcite based support were systematically investigated.It was found that the precursors with good crystallinity and no impurities could be formed under proper MgAl atomic ratio.Weak basic or strong basic precipitation environment was not conducive to the growth of hydrotalcite.CO2-TPD results showed that the strength and number of surface alkaline sites of the sample MAO-10 were similar.The surface of MAO exposed different amounts and positions of OH-and O2-at different calcination temperatures,which affected the distribution of basic sites.The optimized preparation parameters were as follows:the MgAl atomic ratio was 3:1,the precipitation pH was 10,and the calcination temperature was 700℃.The Pd loading was changed to adjust the oxidation site to explore the synergistic effect of the oxidation site and the basic site on the Pd-K-MAO catalyst.It was found that there was an interaction between Pd and K,and the proper loading of Pd could effectively improve the basic distribution and strength of the catalyst.After loading Pd,the catalyst has a variety of basic sites.At the same time,the catalytic reaction of the catalyst in pure N2 shows the existence of multiple oxygen species.Therefore,the Pd-K-MAO bifunctional catalyst can provide abundant basic sites and active oxygen species for the catalytic combustion of soot.Kinetic tests showed that the TOF value of 0.5Pd-K-MAO was the highest,the intrinsic activity was consistent with the apparent activity,and the T10 value was as low as 292℃.Ag-K-MAO series catalysts were prepared in order to investigate the modification effect of basic site on the activity of the catalysts.It was found that Ag0 and Ag+ forms existed on Ag-K-MAO.The presence of Ag+ improves the redox performance of the sample.The presence of Mg(Al)-O-K after the introduction of K led to the emergence of new alkaline sites.Compared with Ag-MAO,Ag-K-MAO has more medium-strong base sites and higher surface oxygen vacancy concentration,which is conducive to oxygen migration.Therefore,in different contact modes and atmospheres,the soot combustion performance of Ag-K-MAO catalyst is excellent,and the lowest T10 can reach 295℃,which provides a technical solution for the development of catalytic particle traps in industry.