Ketonization of Propionic Acid on Lewis Acidic Zr-Beta Zeolite with Improved Stability and Selectivity

Abstract

Ketonization reactions provide a feasible approach to remove oxygen and increase carbon chain length for conversion of biomass derived carboxylic acids. However, the reaction suffers from fast catalyst deactivation and low ketone selectivity. In this work, Lewis acidic heteroatom Ti-, Zr-, Ce-, and Sn-Beta zeolites were prepared using a twostep post-synthesis method and applied in vapor phase ketonization of propionic acid at 350 °C. Among these zeolites, Zr-Beta shows both the highest activity and selectivity. Characterizations indicate that Zr prefers the vacant tetrahedral site when the Zr content is < 7%, corresponding to the maximal fraction of vacant sites produced from dealumination of the parent H-Beta with a Si/Al ratio of 19. Extraframework Zr may also form at a Zr content ≥ 7%. The tetrahedrally coordinated framework Zr species (mainly in the structure of open sites) show Lewis acidic characteristic, and their density can be linearly correlated with the ketonization activity, indicating that these sites are active sites for ketonization. In contrast to rapid deactivation of H-Beta, the 7% Zr-Beta is stable for ketonization over 60 h, maintaining a conversion of ∼50% and a 3-pentanone selectivity > 96% at a space time of 2 h. The amount of coke deposition on Zr-Beta is about 1/3 of that on H-Beta, and the structure of Zr-Beta is preserved after 60 h of reaction. The results of this work indicate that Zr-Beta zeolite is a promising catalyst for ketonization with good stability and high selectivity toward ketone.

Catalytic ketonization of palmitic acid over a series of transition metal oxides supported on zirconia oxide-based catalysts

“…Previous studies have shown that the existence of acidic sites are applicable in the efficacy of ketonization. 65 The balanced Lewis acid–base pairs due to both acid and basic sites facilitates the abstraction of carboxylate ions onto the catalyst surface in either monodentate or bidentate formation each corresponding to weak or intermediate acid sites. 66 In this study, both La 2 O 3 /ZrO 2 and MnO 2 /ZrO 2 show intermediate acidic peaks as observed in Fig.…”

A Review of Recent Research on Catalytic Biomass Pyrolysis and Low-Pressure Hydropyrolysis

“…Because of the large fraction (up to 20 wt %) of reactive aldehydes in the bio-oil, catalysts promoting aldol condensations such as acidic, basic, and acid–base bifunctional catalysts have been investigated . TiO 2 , ZrO 2 , and CeO 2 catalysts are amphoteric and have a high activity for ketonization. − The different crystal phases of TiO 2 , i.e., anatase, rutile, or brookite, impact the catalyst performance in the gas-phase ketonization of carboxylic acids such as acetic acid and propionic acid, and rutile TiO 2 was found to perform best when comparing the activity normalized by surface area . TiO 2 was also found effective in defunctionalizing monomeric methoxy phenolics from lignin into simple phenols, and deoxygenation of whole biomass pyrolysis vapors. ,, Also MnO 2 and La 2 O 3 were found to be active in ketonization. , CFP with ZnO showed only minor improvement of the viscosity and stability of the produced oils. , Besides investigations of impregnating alkali compounds (NaOH, KOH, Na 2 CO 3 , K 2 CO 3 , KC 2 H 3 O 2 , and NaCl) directly into biomass, Na 2 CO 3 supported on γ-Al 2 O 3 or silica–alumina was investigated in ex-situ CFP and found to be highly active for reduction of the acids via ketonization. ,,− …”

Design of Zr- and Al-Doped *BEA-Type Zeolite to Boost LDPE Cracking

“…into their framework. 53 − 55 These heteroatom-incorporated Beta zeolites are often synthesized using dealuminated Beta zeolites. 53 − 55 However, the Brønsted acid sites generated by Al disappear in this method during a dealumination process.…”