Tuning Cooperativity by Controlling the Linker Length of Silica-Supported Amines in Catalysis and CO₂ Capture

Abstract

Cooperative interactions between aminoalkylsilanes and silanols on a silica surface can be controlled by varying the length of the alkyl linker attaching the amine to the silica surface from C1 (methyl) to C5 (pentyl). The linker length strongly affects the catalytic cooperativity of amines and silanols in aldol condensations as well as the adsorptive cooperativity for CO(2) capture. The catalytic cooperativity increases with the linker length up to propyl (C3), with longer, more flexible linkers (up to C5) providing no additional benefit or hindrance. Short linkers (C1 and C2) limit the beneficial amine-silanol cooperativity in aldol condensations, resulting in lower catalytic rates than with the C3+ linkers. For the same materials, the adsorptive cooperativity exhibits similar trends for CO(2) capture efficiency.

Direct synthesis of single-walled aminoaluminosilicate nanotubes with enhanced molecular adsorption selectivity

“…The reaction was performed anhydrously at 900-1,000 psi and 100°C for 5 h. The synthesis details were identical to that described in our previous work. 43 Nanotube synthesis. TEOS and AMTES were mixed with aluminium-tri-secbutoxide in a glove box filled with nitrogen.…”

CO2 Capture and Conversion with a Multifunctional Polyethyleneimine‐Tethered Iminophosphine Iridium Catalyst/Adsorbent

“…[4] Many reactions to convert CO 2 to valueadded products have been reported in the literature, which include CÀC bond formation by reaction with unsaturated hydrocarbons, [2] reaction with alcohols to form carbonates, [1,5] and the direct hydrogenation of CO 2 for formic acid production. [3,[6][7][8][9][10][11][12][13][14][15][16][17][18][19][20][21] Although there are many documented instances of independent CO 2 capture [22][23][24][25][26][27] and CO 2 conversion, [1-3, 5, 6, 9-21] there are few reports that detail the synthesis of materials able to perform both the capture and conversion steps. [28,29] Liu et al prepared a sterically hindered amine (sodium N-alkylgycinate) in poly(ethylene glycol) and showed that it contained a high CO 2 capture capacity.…”

“…[23,24,27,31,32] Moreover, Jones and co-workers demonstrated the impressive CO 2 capture capacity of silicatethered amines and PEI-based materials. [22,[24][25][26] Metal-based catalysts have been supported on polymer backbones in the past. Smith and co-workers have supported Rh and Ir metals on poly(propyleneimine) dendrimer scaffolds.…”

Catalytic Upgrading of Biomass‐Derived Methyl Ketones to Liquid Transportation Fuel Precursors by an Organocatalytic Approach

“…Further support for this conclusion was obtained by noting the absence of activity for Si-Al-C 1 -NHR, ac atalyst in which the linker for the amine group contains only one carbon atom. [16] Therefore, the amine groups must be flexible enough to work cooperatively with the acidic hydroxy groups but spaced far enough from these groups to avoid mutual neutralization of the acid and base groups.B locking the silanol/aluminol groups by silylation using trimethoxysilane decreased the catalyst activity by five times. [17] This observation confirms that acidic sites must work cooperatively with the supported amines to catalyze the selective dimerization of methyl ketones.…”

“…These results suggest that amine-acid site isolation is maintained in Si-Al-supported amine catalyst because protonated amines are known to be less active for condensation reactions. [16] Having established supporteddiamine (-NHCH 2 CH 2 NH 2 ) as the most active catalyst for heptan-2-one dimerization, we examined the effect of varying the density of amines groups on the Si-Al surfaces.A ss hown in Figure 1b,i ncreasing the amine content on the Si-Al surface decreased the catalytic activity.Stated another way,atlow amine loading, an increase in cooperativity between basic sites and silanols/aluminols was achieved by preventing amine aggregation on the Si-Al support surface. [10] We also note that the Si-Al-supported diamine catalyst is remarkably water tolerant and retains its catalytic activity even when the reaction is performed in amixture containing 50 wt %water ( Figure S10).…”