Selective Self‐Condensation of Butanal over Zr‐BEA Zeolites

Abstract

Butanal conversion has been studied over Zr‐BEA zeolites with different amount of partially hydrolyzed open Zr‐sites and fully condensed closed sites. The kinetic study pointed that the main reaction pathway of butanal conversion involves its self‐condensation into 2‐ethyl‐2‐hexenal (2‐EN), the selectivity to 2‐EN being within 80–85 %. Besides, small amounts of 1‐butanol and butanoic acid are formed via Cannizzaro disproportionation of butanal. Secondary reactions include butanoic acid ketonization to 4‐heptanone and esterification to butyl butanoate and tandem hydrogenation/dehydration of 2‐EN into octadienes. A number of techniques, including FTIR spectroscopy of adsorbed CO, pyridine, 2,6‐di‐tert‐butylpyridine (DTBPy), TPD of isopropylamine and selective poisoning with DTBPy were applied for characterization of Zr‐sites and elucidation of their activity. Open Zr‐sites were found to be more active with respect to closed Zr‐sites in butanal condensation: the TOF values estimated at 433 K being 1.4 s−1 for open Zr‐sites and 0.6 s−1 for closed sites. On the contrary, selectivity into 2‐EN was similar for open and closed sites. The results point that Zr‐BEA catalysts with enhanced content of open sites are perspective catalysts for the selective synthesis of 2‐EN.

Catalytic advancements in carboxylic acid ketonization and its perspectives on biomass valorisation

“…This trend is changing however, as this topic has regained new momentum in the last few years. [47,48,69,[116][117][118] A critical first aspect for discussion is the nature of the catalytic active sites, the reaction mechanism and how these differ from metal oxide materials. While there seems to be a general consensus regarding the active sites and activation of the first carboxylic acid, uncertainty still surrounds the exact nature of the rate-limiting step and activation of the second acid molecule.…”

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

“…The estimated LAS density is in agreement with the theoretical value of 767 μmol/ g estimated from the Zr content. This result reflects that most Zr have incorporated into the BEA framework with a tetrahedral structure, 68 which forms LAS. Zr-Beta two types of Lewis sites, i.e., open and closed sites (Scheme 1).…”

“… To probe the structure of LAS of Zr-Beta synthesized by the SSIE method, the IR experiment of DTBPy adsorption was performed, since DTBPy exclusively adsorbs on weakly acidic −OH groups of open sites . As shown in Figure C, bands at 1614 and 3365 cm –1 can be ascribed to protonated DTBPy . The band at 3365 cm –1 is assigned to ν­(N-H + ), and its integrated intensity has been used to estimate the density of the open sites by using the extinction coefficient reported by Ivanova and co-workers .…”

“…70 As shown in Figure 5C, bands at 1614 and 3365 cm −1 can be ascribed to protonated DTBPy. 68 The band at 3365 cm −1 is assigned to ν(N-H + ), and its integrated intensity has been used to estimate the density of the open sites by using the extinction coefficient reported by Ivanova and co-workers. 68 The estimated density of open sites is 606 μmol/g for 7% Zr-Beta, accounting for 92.5% of total LAS derived from the pyridine adsorption.…”

“…68 The band at 3365 cm −1 is assigned to ν(N-H + ), and its integrated intensity has been used to estimate the density of the open sites by using the extinction coefficient reported by Ivanova and co-workers. 68 The estimated density of open sites is 606 μmol/g for 7% Zr-Beta, accounting for 92.5% of total LAS derived from the pyridine adsorption. This result indicates that the most of the LASs of Zr species in 7% Zr-Beta are open sites and serve as active sites for ketonization of propionic acid.…”