Effects of crystal size, acidity, and synthesis procedure on the catalytic performance of gallium and aluminum MFI zeolites in glycerol dehydration

Abstract

The influence on gas-phase catalytic glycerol dehydration of crystal size (S: small, or L: large crystals), acidity, and synthesis procedure for isomorphous incorporation of gallium (Ga-S; Ga-L) or aluminum (Al-S; AlL) in MFI zeolites was studied. The main product observed was acrolein, with the undesirable parallel formation of deactivating coke molecules such as polyglycols and polyaromatics. The GaS zeolite showed the best performance in this reaction, as it provided a combination of adequate accessibility to the microporous system and weak Brønsted acid sites. The chemical and structural properties of the fresh MFI zeolites were studied by X-ray diffraction, nitrogen sorption measurements, scanning electron microscopy, temperature-programmed desorption of NH 3 , X-ray photoelectron spectroscopy, and 27 Al and 29 Si MAS-NMR. Solid-state 13 C MAS-NMR and thermogravimetric analyses of the spent MFI zeolites confirmed the differences in the nature and amounts of the carbonaceous deposits formed. The polyglycols were preferentially formed on the external surface of the zeolite crystals, as expected due to the greater exposed area. On the other hand, the polyaromatic compounds formed were more abundant inside the micropores of the MFI zeolites, especially those composed of larger crystals and with a greater number of strong Brønsted acid sites.

Gallium Modified HUSY Zeolite as an Effective Co‐support for NiMo Hydrodesulfurization Catalyst and the Catalyst's High Isomerization Selectivity

“…The activation energies of 4,6-DMDBT HDS reactions over all the mentioned catalysts at 563 Kw ere calculated by employing ap seudo-first order reaction according to Equation (5) [30,33] by fixing the LHSV at 40 h À1 and varying the reaction temperature in the range of 558 Kto5 73 Katan interval of 5K:…”

“…Thus, we modified HUSY (hydrogen ion exchanged ultra-stable Y) zeolites with gallium as ac o-support for ah ydrotreatingc atalyst. After HUSY zeolites are modified by gallium,s ome of the Si-O(H)-Al bonds can be substituted by Si-O(H)-Ga bonds [30] because the Ga-O(H)-Si sites are more covalentt han the Al-O(H)-Si sites. Moreover,t he averagee lectronegativity value of 1.59 for Ga is lower than the value for Al (1.714), [31] implyingalower acid strengtho fB rønsted protons for Ga-substituted zeolites.…”

Acetalization of glycerol with acetone over various metal-modified SBA-15 catalysts

“…It is a process of transesterification of triglycerides with methanol in the presence of acidic or basic catalysts. Biodiesel has been considered to be one of the most promising alternatives to fossil fuel resources [1][2][3][4]. In addition, the process produces substantial amounts of glycerol as the main by-product, which is equivalent to 10 wt% of the total biodiesel production [5].…”

The multiple benefits of glycerol conversion to acrolein and acrylic acid catalyzed by vanadium oxides supported on micro-mesoporous MFI zeolites

“…For glycerol dehydration using zeolites, maximum performance of the catalyst is achieved by combining Brønsted acid sites of medium strength (strong acid sites lead to severe coke formation, http://dx.doi.org/10.1016/j.cattod.2016.08.005 0920-5861/© 2016 Elsevier B.V. All rights reserved. while weak acid sites are less capable of converting glycerol) [27], porosity (which enhances the diffusion of glycerol and acrolein), and high specific area (which increases access to catalytic sites). For instance, members of the lamellar MWW zeolite family, which includes microporous MCM-22, pillared MCM-36, and delaminated ITQ-2, offer advantageous characteristics for glycerol dehydration [22].…”