H- and Cu- Forms of MFI Boralites with Enhanced Number of Skeletal Boron Atoms. Synthesis and Properties

Abstract

Abstract Preparation, physico-chemical properties and catalytic activity in the selective reduction of NO are described for CuH-[B]ZSM-5 metallosilicates with relatively high number of B atoms inside the skeleton and, consequently, unusually small unit cell. Na content is so small that Na+compensation of skeleton charge can be neglected. It is shown that Cu ions are introduced into the boralites directly during the synthesis if tetrapropylammonium TPA+template is replaced by ethylamine which forms complexes with Cu2+. These complexes are located inside the boralite channels together with protonated ethylamine, and on the outer surface of zeolite grains. EAH+is easily decomposed already at 200°C while EA ligands on Cu2+are removed at 350-400°C. The decomposition in oxygen (at 450°C) and the rehydration are accompanied with the migration of Cu2+ions from the outer surface to the interior where they remain in the form of isolated and small oxidic species. Simultaneously, some of the tetrahedral B atoms change the coordination to the trigonal one. The Cu samples prepared by direct synthesis are compared with (EA)-boralites impregnated with Cu2+and with CuH-boralites prepared by ionic exchange. Synthesized Cu boralites were found to be good catalysts for selective reduction of NO by ammonia to N2.