Transalkylation of C10 aromatics with 2-methylnaphthalene for 2,6-dimethylnaphthalene synthesis: High-efficiently shape-selective & synergistic catalysis over a multifunctional SiO2-Mo-HBeta catalyst

Transalkylation of C10 Aromatics with 2-Methylnaphthalene for 2,6-Dimethylnaphthalene Synthesis over a Shape-Selective SiO2–Ni–H-Mordenite with Nanosheet Crystal

“…However, significantly decreased naphthalene nucleus loss and polyalkylnaphthalene output were both also observed especially over SiO 2 (II)- or SiO 2 (III)-modified sample without external acidity. According to the conclusion in our previous research, this is because the side reactions of naphthalene nucleus hydrogenation ring opening and MN polyalkylation involved in large-molecule intermediates mainly take place on the external surface of Ni–HMOR, while they almost cannot occur inside the 12-ring pores with shape-selectivity restriction . Besides, the higher contents of naphthalene and 1-methylnaphthalene in products were observed over SiO 2 –3.0%Ni–HMOR with more cycle times for SiO 2 deposition.…”

“…It has been widely accepted that transalkylation is catalyzed by the strong acid sites over zeolites. ,− However, as seen in the detailed results of transalkylation listed in Table S2, compared with parent HMOR, the Ni-modified samples with lower densities of strong acid sites (especially 3.0%Ni–HMOR and 6.0%Ni–HMOR) showed significantly increased 2-MN conversion and 2,6-DMN yield. According to conclusions in previous literature, the transalkylation of C 10 A with naphthalene/methylnaphthalene over a metal-modified zeolite with the capacity of catalytic hydrogenation may likely be according to the following pathway catalyzed mainly by protonic acid sites: the alkyl (such as ethyl, propyl, butyl) carbocations originated from C 10 A react with naphthalene/methylnaphthalene and then dimethylnaphthalene is formed through subsequent side-chain dealkylation of dialkylnaphthalenes. , The greatly improved reactivity of transalkylation in this work is likely due to the formation of active hydrogen species on the surface of Ni–HMOR in a H 2 atmosphere at high pressure . Concretely, hydrogen molecules are adsorbed to the active surface of metal Ni nanoclusters and are dissociated into hydrogen atoms.…”

“…The deactivation of zeolite catalyst in this transalkylation is mainly caused by coke deposition which blocks channels and then inhibits the diffusion of molecules. , Thus, one important reason for the much higher catalytic stability of 3.0%Ni–HMOR in the H 2 atmosphere is the surface catalytic hydrogenation. It can immediately convert almost all olefins (produced from cracking and C 10 A dealkylation) into alkanes and thus prohibit the olefin oligomerization which can result in the formation of larger coke molecules. , This is powerfully supported by the analysis results of the aliphatic distribution in the reaction tail gas under different catalytic conditions. As shown in Table S3, the aliphatic byproducts over Ni-containing samples in the H 2 atmosphere were almost only alkanes and negligible olefins, while there were much higher proportions of olefins and C 4+ aliphatics in the aliphatic byproducts for the Ni-containing zeolite under the N 2 atmosphere or the parent HMOR.…”

“…On the one hand, the reasonable hydrogenation catalyzed by internal metal Ni active sites effectively suppressed the formation of olefins (as listed in Table S3), macromolecular polymers, polycyclic aromatic hydrocarbons, etc. (as shown in Figure ) and then significantly inhibited the rapid coke deposition in shape-selective channels . On the other hand, this catalyst had an impressive capability of accommodating coke, attributed to its lamellar crystals which had both a much shorter diffusion-reaction path in the microporous system and the large external surface area and considerable stacking mesopores …”

“…All these seriously impede its development for industrial application, meaning this synthesis route still has obvious disadvantages. In previous work, we developed a low-cost process route for 2,6-DMN synthesis through the transalkylation of C 10 aromatics (C 10 A) with 2-MN over zeolite catalyst, by using the low-priced C 10 A as solvent and transalkylation reagent. The new reaction system involved in large-size molecules such as C 10 A demands both high diffusibility and reasonable acid properties for the catalyst.…”