Heteronuclear NMR Correlations To Probe the Local Structure of Catalytically Active Surface Aluminum Hydride Species on γ‐Alumina

Abstract

International audienc

Well-defined silica supported aluminum hydride: another step towards the utopian single site dream?

“…The signal at 26 ppm assigned to Al–CH 2 – C H–( C H 3 ) 2 is no longer detected. The broad 1 H signal at 4.3 ppm is attributed to Al– H , 43 Si– H and Si H 2 . 55 , 56 , 68 …”

“…43 We were interested in the formation of aluminum hydride species through a variable temperature treatment (100 °C to 400 °C, rate 60 °C h –1 , Fig. S8 and S9, ESI†) under high vacuum (10 –5 mbar).…”

“…Aluminum hydride have been already formed on γ-alumina but the process required harsh temperature conditions (400 °C) under H 2 pressure of 0.733 bar. 43 We were interested in the formation of aluminum hydride species through a variable temperature treatment (100 °C to 400 °C, rate 60 °C h –1 , Fig. S8 and S9, ESI † ) under high vacuum (10 –5 mbar).…”

“…8 ). 43 , 67 They are easily attributed to the vibration bands of Al–H. Indeed, terminal Al–H elongation bands range down to 1800 cm –1 , bridging Al–H–Al give rise to signals between 1750 and 1550 cm –1 .…”

Rationalization of solid-state NMR multi-pulse decoupling strategies: Coupling of spin I = ½ and half-integer quadrupolar nuclei

“…The choice of decoupling scheme depends upon the type of heteronuclear interactions that broadens the spectral lines [15,16]. It has been shown that the heteronuclear scalar coupling between nuclei with spin quantum number I = ½ spin and surrounding quadrupolar nuclei (I > 1/2) with half-integer spin quantum number can dramatically decrease the spectral resolution and hinder the extraction of structural and chemical information [16][17][18][19][20][21]. Although the heteronuclear dipolar coupling can, in principle, be averaged by MAS, the introduction of other time-dependent phenomena, such as RF irradiation (as applied during a decoupling sequence for example), can lead to an interference effect if the two happen on a similar timescale.…”