Functionalization of zeolitic cavities : Grafting NH2 groups in framework T sites of B-SSZ-13 A way to obtain basic solids catalysts?

Insertion of B atoms into an Al-free zeolitic framework with CHA topology results in the formation of B-SSZ-13 zeotype with Si/B = 11. B K-edge NEXAFS testifies that B forms [B(OSi) 4 ] units in a T d -like geometry (sp 3 -hybridized B atoms). According to B K-edge NEXAFS and IR, template burning results in the formation of [B(OSi) 3 ] units in a D 3h -like geometry (sp 2 -hybridized B atoms) with a break of a B-O-Si bond and the formation of a Si-OH group. The activated material contains B(lll) Lewis acid centers able to specifically coordinate bases like NH 3 . Such [B(OSi) 3 ] units are reactive toward ammonia, resulting in the formation of B-NH 2 surface functionality inside the pores of B-SSZ-13 already under mild conditions, i.e., 35 mbar of NH 3 at 373 K for 30 min and without crystallinity degradation. A minor fraction of Si-NH 2 cannot be excluded owing to the presence of two IR doublets at 3500 and 3430 cm -1 and at 1600 and 1550 cm -1 . Ab initio B3LYP/6-31+G(d,p) calculations on a cluster model, supported by a single-point MP2 on B3LYP/6-31+G(D,P) optimized structures, found the break by NH 3 of a B-O-Si bond of the [B(OSi) 3 ] unit with formation of [SiOH] and [H 2 N-B(OSi) 2 ] species to be energetically favored. Comparison between experimental and computed frequency shifts shows them to be in semiquantitative agreement. The high stability of the B-NH 2 surface functionality is probed by N K-edge NEXAFS spectra collected under UHV conditions. These findings can open a new route in the preparation of shape selective solid basic catalysts.