The Promotional Effects of CsNO3 on Sn-Co-O Solid Solution for Soot Combustion: Using XRD Extrapolation Method to Elucidate the Structure-reactivity Relationship

Abstract To fabricate more feasible catalysts for soot oxidation, CsNO3 was used to promote a tetragonal rutile SnO2 solid solution support doped by Co3O4. To select a suitable support, an XRD extrapolation method was adopted to identify the lattice capacity of Co2+/Co3+ cations in SnO2 matrix, which is 0.0934 g Co3O4/g SnO2. The sample with the lattice capacity quantity of Co cations (SC85-15) forms the largest amount of pure solid solution phase, and has the biggest surface areas in all the samples, thus being selected as the support for CsNO3. To understand the structure-reactivity relationship, the XRD extrapolation method has also been adopted to measure the monolayer dispersion threshold of CsNO3 on the SC85-15 support, which is 0.644 mmol per 100 m2 surface. Below the threshold, CsNO3 is present as sub-monolayer/monolayer phase. Above the threshold, CsNO3 micro crystallites are also formed. It has been substantiated that by adding CsNO3 onto the surface of the SC85-15 support, active electrophilic O2- and O22- anions can be effectively formed, which determine the soot combustion activity. Due to presence of the largest amount of surface O2- and O22- sites, the catalysts with 8% CsNO3 exhibits the best activity in all the catalysts.