Improved Transalkylation of C10 Aromatics with 2-Methylnaphthalene for 2,6-Dimethylnaphthalene Synthesis over Pd-Modified Zeolites with Different Framework Structures,Industrial & Engineering Chemistry Research

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Improved Transalkylation of C10 Aromatics with 2-Methylnaphthalene for 2,6-Dimethylnaphthalene Synthesis over Pd-Modified Zeolites with Different Framework Structures
Industrial & Engineering Chemistry Research ( IF 3.8 ) Pub Date : 2024-07-12 , DOI: 10.1021/acs.iecr.4c01976
Junhui Li ₁ , Ziliang Liao ₁ , Wenzhi Jia ₂ , Zhirong Zhu ₁

Affiliation

Here, Pd-HMCM-22, Pd-HBeta, Pd-HMOR, and Pd-HZSM-5 zeolites were prepared and, respectively, tested as catalysts in the transalkylation of C₁₀ aromatics (C₁₀A) with 2-methylnaphthalene (2-MN) for synthesizing 2,6-dimethylnaphthalene (2,6-DMN). Each one of these Pd-zeolites exhibited a significantly improved transalkylation reactivity (compared with its parent precursor) in H₂ reaction atmosphere, likely attributed to a hydrogen spillover from metal Pd to zeolite and the subsequent generation of surface-active hydrogen species, which greatly enhanced the proton-transfer efficiency in the surface transalkylation catalyzed by strong protonic acid sites. Meanwhile, it is speculated that the surface-active hydrogen species also accelerated the secondary DMNs’ isomerization and simultaneously caused a coincident increase in the selectivities (in DMNs) of 2,6-DMN and β,β-DMNs with a higher diffusion rate in pores or pockets. The 0.1 wt % Pd-HBeta with 12-ring large pores, more strong Brönsted acid sites, a high Lewis acid density, and a higher palladium dispersion showed a higher 2-MN conversion, DMN selectivity, and 2,6-DMN yield than those of the other three 0.1 wt % Pd-modified zeolites. Because of the strong protonic acid density, the Pd dispersion of 0.1 wt % Pd-HMCM-22 or 0.1 wt % Pd-HMOR was lower, and 0.1 wt % Pd-HZSM-5 had a lower palladium dispersion and a repulsion of its smaller pores to C₁₀A reactants. Moreover, the reasonable distributions of metal-Pd sites and acidity on the 0.1 wt % Pd-HBeta catalyst not only prevented the severe naphthalene ring loss resulting from the side reactions of hydrogenation and subsequent ring opening and cracking, but also endowed it with a remarkably improved catalytic stability due to the fact that a reasonable catalytic hydrogenation effectively suppressed the formation of large coke molecules and restrained a fast coke deposition. Finally, the 2-MN conversion of >81% and the 2,6-DMN yield of >9.8% were obtained over 0.1 wt % Pd-HBeta during a 25 h on-stream reaction, depending on both an efficient internal diffusion of reactants/products in its three-dimensional 12-ring pores, where enough active sites were accessible, and a high-efficiency surface-concerted catalysis of metal-Pd sites and acid sites.

中文翻译：

不同骨架结构的 Pd 改性沸石上改进 C10 芳烃与 2-甲基萘的烷基转移合成 2,6-二甲基萘

在此，制备了 Pd-HMCM-22、Pd-HBeta、Pd-HMOR 和 Pd-HZSM-5 沸石，并分别作为 C ₁₀ 芳烃（C ₁₀ A)与2-甲基萘(2-MN)合成2,6-二甲基萘(2,6-DMN)。这些 Pd-沸石中的每一种在 H ₂ 反应气氛中都表现出显着改善的烷基转移反应性（与其母体前体相比），这可能归因于氢从金属 Pd 溢出到沸石以及随后生成的表面-活性氢物种，大大提高了强质子酸位点催化的表面烷基转移的质子转移效率。同时，推测表面活性氢物种也加速了二级DMNs的异构化，同时导致2,6-DMNs和β,β-DMNs的选择性（以DMNs计）同时增加，并且在DMNs中具有更高的扩散速率。毛孔或口袋。 0.1 wt% Pd-Hβ 具有 12 环大孔、更强的布朗斯台德酸中心、高路易斯酸密度和更高的钯分散度，与其他三种 0.1 wt% Pd 改性沸石的那些。由于质子酸密度较强，0.1 wt% Pd-HMCM-22 或 0.1 wt% Pd-HMOR 的钯分散度较低，0.1 wt% Pd-HZSM-5 的钯分散度较低，其排斥力较小。 C ₁₀ A 反应物的孔。此外，金属Pd位点和酸度的合理分布在0.1 wt% Pd-Hβ催化剂不仅防止了加氢副反应以及随后的开环裂化导致的严重萘环损失，而且由于合理的催化加氢有效抑制了其催化稳定性，使其具有显着提高的催化稳定性。形成大的焦炭分子并抑制焦炭的快速沉积。最后，在 25 小时的在线反应过程中，在 0.1 wt% Pd-HBe 上获得了 >81% 的 2-MN 转化率和 >9.8% 的 2,6-DMN 产率，这取决于反应物的有效内部扩散/产品位于其三维12环孔中，其中有足够的活性位点，以及金属-Pd位点和酸位点的高效表面协同催化。

更新日期：2024-07-12

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