Geminal Coordinatively Unsaturated Sites on MOF‐808 for the Selective Uptake of Phenolics from a Real Bio‐Oil Mixture

Abstract

The capping formate anions of the metal–organic framework (MOF) zirconium benzene‐1,3,5‐tricarboxylate (MOF‐808) were removed by a solvent exchange procedure, resulting in a formate‐free MOF‐808 sample containing “geminal” defects consisting of six coordinatively unsaturated sites (CUSs) on each of the Zr6 nodes. Adsorption experiments with this material showed that the uptake of 4‐methylguaiacol from a bio‐oil mixture was proportional to the number of defects and amounted to one mole adsorbed per mole of zirconium. The selective uptake behavior of MOF‐808 towards phenolic compounds was further evident from competitive adsorption experiments between furfuryl alcohol and 4‐methylguaiacol as well as from the excellent (20 wt % for phenolic compounds and <7 wt % for other compounds) uptake performance for real bio‐oil mixtures containing a large concentration and diversity of molecules.

Zr‐MOF‐808 as Catalyst for Amide Esterification

“…Benzoic acid would be formed as a result of benzamide or butyl benzoate hydrolysis. Furthermore, that exchange could be facilitated by the polar solvent ( n‐ BuOH) employed in the reaction, as has been reported previously por Zr‐MOF‐808 when using methanol [54] . That structural change is also observed in the PXRD data measured in the five‐times‐used catalyst, showing differences in signal intensities and increased FWHM compared to the fresh Zr‐MOF‐808‐P.…”

“…Moreover, when these samples were pre‐treated at 250 °C under high‐vacuum (Figure 8 c and d) for release of formate linkers [54] and/or dehydroxylation of the cluster, [56] two bands are identified at 2155 cm −1 , corresponding to the interaction of CO with Brønsted acid sites, and at 2177 cm −1 , being assigned to Lewis acid centers. This means that one of the types of Brønsted acid sites was lost with the dehydroxylation, generating Lewis acid sites.…”

“…From these calculations, it can be concluded that Zr‐MOF‐808‐P possesses a relative amount of acid centers slightly higher than Zr‐MOF‐808 for dehydroxylated formula (Table 3). Furthermore, the number of BTC linkers was determined by TGA analysis [54] (see Supporting Information, section 2.2.2.) finding that Zr‐MOF‐808‐P presents 1.7 linkers versus 1.9 BTC linkers detected for Zr‐MOF‐808 revealing a higher degree of defects for the Zr‐MOF‐808‐P framework.…”

Síntesis de catalizadores sólidos orgánicos e híbridos orgánicos-inorgánicos y su aplicación

“…Sin embargo, el último tramo descrito (la región III) permite conocer el número de ligandos orgánicos por fórmula molecular de cada catalizador. 112,113,114,115 En general, los MOFs-808 (3:1) presentan más defectos que los MOFs-808 (1:1) en su estructura. Es decir, el número de ligandos en la estructura es menor cuando se disminuye la proporción de ligando durante la preparación del material, aunque este descenso no es proporcional al porcentaje de ligando reducido en la mezcla reactiva.…”

“…Cuando se realiza un pretratamiento a una mayor temperatura, es posible producir la deshidroxilación de los clústeres de zirconio 126 y/o eliminar los ligandos del modulador. 115 En la secuencia de espectros FT-IR diferencia para los MOFs-808-Zr se identifican cuatro bandas: a 2177 cm -1 (que se asigna a los centros con acidez de Lewis), a 2155 cm -1 (que corresponden a la interacción del CO con los centros con acidez de Brönsted), a 3600 cm -1 (está asociada con la segunda) y, finalmente, a 2138 cm -1 (relacionada con la fisisorción de CO). Por lo tanto, uno de los tipos de sitios ácidos de Brönsted se pierde con la deshidroxilación, generando los centros ácidos de Lewis.…”