Amine-Functionalized Ordered Mesoporous Silica Transesterification Catalysts

Abstract

The synthesis, characterization, and catalytic behavior of several amine-functionalized ordered mesoporous silica (OMS) materials are reported. All samples show catalytic activity for the conversion of glyceryl tributyrate with methanol to methyl esters in high yield (>60%). The reactivity of the amines approximately correlates with the pK values of the free amines. The effect of the amine identity, loading, and substrate pore size is also reported. To determine if leached amine was responsible for the observed reactivity, the hot filtrate method was employed. Those experiments show that upon removal of the OMS material the reaction conversion does not increase, indicating surface-tethered amines are primarily responsible for the observed reactivity. The stability of the most promising catalyst, 3-(anilinopropyl)-MCM-41 was analyzed via recycle studies. Leaching of the amine is observed via a decrease in conversion with multiple recycles and a concomitant change in sample color. Capping the residual silanols groups with hexamethyldisilazane leads to an increase in the catalyst stability with a decrease in activity. The work indicates that these solids are interesting alternatives to conventional homogeneous catalysts for this class of chemistry.

A Series of UiO-66(Zr)-Structured Materials with Defects as Heterogeneous Catalysts for Biodiesel Production

“…UiO-66­(Zr)-NH 2 -green is the best one in the current esterification reaction owing to the existence of both acidic and basic sites, besides a large pore volume accessible to accommodate the reactants and activate the reaction . It has been reported that basic catalysts like functionalized silica with amine , and carbon nanotubes are highly efficient in biodiesel production. Actually, utilizing UiO-66­(Zr)-NH 2 in esterification of oleic acid with methanol at room temperature and maintaining the other above mentioned conditions also give a high yield of FAME (81.8 %).…”

Valorization of rice husk silica waste: Organo-amine functionalized castor oil templated mesoporous silicas for biofuels synthesis

“…The higher activity of the MT-RHS is attributed to improved mass transport and amine accessibility, while the higher TOF of the tertiary amine is attributed to its fractionally stronger basicity. [42][43][44][45] The maximum TOF of 140 h -1 for the DEPA-MT-RHS catalyst compares favorably with recent reports for other solid bases including nano-MgO (84 h -1 ), [46] MgO-ZrO 2 (100 h -1 ), [47], [48] and a Mg 3 Al hydrotalcite (60 h -1 ), [49] but is less than observed for macroporous Mg-Al hydrotalcites (376 h -1 ) for which mass transport is extremely efficient. [50] Recycle tests for DEPA-MT-RHS evidenced modest catalyst stability, with only a 10 % decrease in conversion following the first re-use ( Figure S6), albeit dropping by 50 % after five re-uses.…”

Mesoporous Silica-Based Catalysts for Biodiesel Production: A Review

“…The surface basicity modification of mesoporous silica is usually performed by anchoring alkylamine and other nitrogen ligands, and the immobilization of alkali/alkali earth oxide such as CaO, MgO, and Li 2 O [45,52,53,55]. The modification of mesoporous silica with 3-aminopropyltriethoxysilane (RNH 2 ), 2,3-aminoethylamino)propyltrimethoxysilane (NN), and 3-diethylaminopropyltrimethoxysilane (DN) showed increased basicity, which related to the increasing turn-over number.…”