Enhancement of the NH_3-SCR property of Ce-Zr-Ti by surface and structure modification with P

摘要

The P-x-Ce-0.3-Zr-Ti catalysts were prepared by hydrothermal method and the effect of P modification on NH3-SCR property and structure was investigated. The P-0.15-Ce-0.3-Zr-Ti catalysts showed an excellent NH3-SCR activity in wide temperature range (Over 80% NOx conversion at 180-400 degrees C). Surprisingly, some nano-hollow spheres structures formed in P-0.15-Ce-0.3-Zr-Ti catalysts by introducing appropriate amount of H4P2O7, greatly increasing the specific surface area of catalysts and providing more reaction sites for active gases. And further characterizations indicated that there existed a new substance CePO4 in catalysts. With the increase of surface Ce3+, the redox ability of catalysts was greatly improved, resulting in a better catalytic activity at low temperature. Meanwhile, the catalysts modified by H4P2O7 produced more surface active oxygen species and other defects, as well as more surface acid sites, which played an important role in catalytic activity within a wide temperature window. DRIFTS results suggested that modification with P could promote the formation of NO2 and mono dentate nitrates, thereby enhancing SCR reaction process (Langmuir-Hinshelwood reaction pathway). Besides, the presence of amide species (-NH2) is an important marker for the catalyst to follow the E-R reaction mechanism.