A review on pillared clay-based catalysts for low-temperature selective catalytic reduction of NOx with hydrocarbons

Abstract

Strict air pollution restrictions have increased the need for effective low-temperature selective catalytic reduction (LT-SCR) of NOx with hydrocarbons (HC), and as such, mixed metal oxides and clay minerals supported catalysts have received significant attention. Pillared interlayered clay (PILC) materials use clay mineral as a raw material for catalyst support coupled with metal oxide particles to provide a porous structure between clay mineral layers through ion exchange. PILC has been widely used in catalysis and adsorption applications, due to its meso-microporous structure, good surface acidity, large specific surface area, adjustable pore size, interlayer ion-exchange nature, and good thermal stability. It is a widely used catalyst carrier material with excellent performance for LT-SCR of NOx with HC. Notably, the montmorillonite (Mt) based Cu- and Fe-PILC catalysts exhibited a high LT-SCR activity, which can be assigned to the excellent redox capability of the co-existing FeIII/FeII and CuII/CuI. In addition, the presence of CuII isolated species, as well as the strong interaction between Fe, Cu, and PILC support is believed to increase the SCR activity. This review study is primarily focused on the clay mineral importance and Mt-based PILC-supported catalysts for LT-SCR of NOx with HC. In addition, the SCR performances of various metals-supported PILC-based catalysts were compiled, in order to study their proposed reaction mechanisms, the influence of metal loading, effects of O2, H2O, and SO2 poisoning for HC-SCR of NOx conversion. This study provides a detailed review of Mt-based PILC catalysts for LT-SCR technology, including recent challenges and future prospects.