Pore Blocking by Phenolates as Deactivation Path during the Cracking of 4-Propylphenol over ZSM-5

Abstract

Cracking of propyl side chains from 4-propylphenol, a model compound for lignin monomers, is studied for a commercial ZSM-5 zeolite catalyst. The decline of 4-propylphenol conversion with time on stream can be delayed by co-feeding water. FTIR spectroscopy shows the formation of chemisorbed phenolates during reactions and significant amounts of phenolics are detected by GC-MS of the extract from the spent catalysts. Thus, chemisorbed phenolates are identified as the main reason for deactivation in the absence of water. Regardless of the amount of co-fed water, substituted monoaromatics and polyaromatic species are formed. Comprehensive characterization of the spent catalysts including Raman and solid-state 27Al NMR spectroscopy, and thermogravimetric analysis points to a combination of deactivation processes. First, phenolates bind to Lewis acid sites within the zeolite framework and hinder diffusion unless they are hydrolyzed by water. In addition, light olefins created during the cracking process react to form a polyaromatic coke that deactivates the catalyst more permanently.

Mechanocatalytic hydrogenolysis of benzyl phenyl ether over supported nickel catalysts

“…Aer 180 min, catechol, phenol, and cyclohexanol were detected at similar yields as HDO products during the hydrogenolysis of BPE (<1%), while the carbon balance was slightly lower (62% compared to 77%). Future work will focus on adapting reaction engineering strategies, such as simultaneous hydrolysis, 64 to desorb phenolates or the use of redox active catalysts, 65,66 to recover adsorbed products and prevent further side reactions.…”

Reaction Mechanism of Tetrahydrofurfuryl Alcohol Hydrogenolysis on Ru/SiO2 Studied by In‐Situ FTIR Spectroscopy

“…In the most common approach, a pulse of the molecule of interest is admitted into a cell containing the activated catalyst, and the surface reactions of the molecule are followed [22–30] . Pulse studies have been performed with reasonably complex molecules, such as ethyl pyruvate [23] or phenol [31] . However, they are not well representative for catalysts under reaction conditions as the surface coverage may differ and fresh reactant is continuously fed to the catalyst surface.…”

“…[22][23][24][25][26][27][28][29][30] Pulse studies have been performed with reasonably complex molecules, such as ethyl pyruvate [23] or phenol. [31] However, they are not well representative for catalysts under reaction conditions as the surface coverage may differ and fresh reactant is continuously fed to the catalyst surface. Studies that monitor the surface reaction with respect to time on stream at a constant temperature are important but generally only performed for 'simple' reaction systems that use small molecules as reactants, such as CO, CO 2 , NH 3 , CH 4 , MeOH, EtOH or propanal.…”

Characterization of Surface Species during Benzene Hydroxylation over a NiO-Ceria-Zirconia Catalyst

“…However, a mechanistic study of benzene hydroxylation on a Cu/HZSM5 zeolite found that inefficient product desorption and poisoning on these materials can be major challenges due to the strong adsorption of benzene on the metal centers . Similarly, catecholates and phenolates have been shown to strongly chemisorb on zeolites creating diffusional barriers that deactivate catalysts during biomass conversion. , …”

“…20 Similarly, catecholates and phenolates have been shown to strongly chemisorb on zeolites creating diffusional barriers that deactivate catalysts during biomass conversion. 21,22 The similarities in the direct partial oxidation chemistries of methane and benzene suggest that Lewis-acidic NiO clusters on redox active ceria-based supports, which can activate methane, 23−26 could also catalyze benzene hydroxylation. Indeed, experimental and theoretical studies have shown that Lewis-acidic NiO active centers can perform benzene activation and hydroxylation.…”