Abstract
AbstractDeveloping efficient solid catalysts is necessary when for example moving from batch chemistry to continuous flow systems. In this work, scale‐up effects of zeolite‐based catalyst materials have been tested in aldol condensation as a model reaction for bio‐oil upgrading via deoxygenation. For this purpose, shaped catalyst bodies were obtained via extrusion of ultrastable Y zeolite (USY) using either attapulgite (Att.) or bentonite (Bent.) as clay binder, followed by post‐alkali metal ion grafting of K+ after (rather than before) extrusion. This approach proved essential to preserve the catalysts’ crystallinity. The Att.‐bound catalyst body was more active than its Bent.‐counterpart, correlating well with the observed changes in physicochemical properties. The K‐(USY/Att.) catalyst showed new basic oxygen and strong Lewis acidic sites resulting from clay incorporation, in addition to the Lewis acid (K+) and basic sites (K−OH) created upon grafting. For K‐(USY/Bent.), the grafting proved less efficient, likely due to pore blockage caused by the binder. Bent. addition resulted in acid sites of moderate Brønsted and strong Lewis acidity, but hardly any of the basicity desired for the aldol condensation reaction. The poor potassium grafting yet led to some cation exchange with the binder (likely with the Na+ naturally present in the Bent. material). The results obtained demonstrate the critical importance of the choice of the binder material and the synthesis protocol adopted for upscaling solid base materials in the form of catalyst bodies.
Highlights
Developing efficient solid catalysts is necessary when for example moving from batch chemistry to continuous flow systems
Bent. addition resulted in acid sites of moderate Brønsted and strong Lewis acidity, but hardly any of the basicity desired for the aldol condensation reaction
We explore the extrusion of ultrastable Y zeolite (USY) zeolite with attapulgite and bentonite as binder materials and the incorporation of potassium by grafting in an alcoholic medium
Summary
Different alkaline metals and synthesis conditions tested, treatment of zeolite USY with 0.1 M KOH in methanol led to the most active and stable catalytic material for the vapor-phase aldol condensation of propanal (which was selected as model reaction for bio-oil upgrading).[8,9] Keller et al reported excellent activities, as well as stability with increasing time-on-stream and selectivities of 90 % towards the desired pathway, with only limited activity towards the competitive Tishchenko reaction,[13] which is favored by stronger bases Likewise, this catalytic system has been coupled in series with a zeolite ZSM-5-based catalyst, showing its high activity for aldol condensation and ketonization reactions, as well as for the conversion of oligomers in bio-oil, producing liquid organic fractions with low oxygen content.[14] These promising results encouraged the study of shaped K-grafted USY catalysts to evaluate the scalability of this technology for potential use in industrialscale reactors. The impact of the synthesis protocol has been evaluated, i. e., pre- vs. post-grafting on the physicochemical properties of the USY-clay catalyst body
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