n-Propylbenzene Disproportionation: An Efficient Tool for Assessing the Framework Topology of Large-Pore Zeolites

Abstract

The mechanisms of n-propylbenzene (nPB) disproportionation over various large-pore (LaNa-Y, H-Y, H-mordenite, and H-beta) and medium-pore (H-NU-87, H-TNU-9, and H-ZSM-5) zeolites were investigated. The GC–MS results from the used zeolite catalysts demonstrate that monopropylated 1,1-diphenylpropane and dipropylated 1,1-diphenylpropane derivatives are serving as the main reaction intermediates of bimolecular nPB disproportionation, whereas 1-phenyl-2-propylphenylpropane, 1-propylphenyl-2-phenylpropane, and 1-propylphenyl-2-propylphenylpropane species are the intermediates of some particular side reactions. It was found that the intrazeolitic buildup of these five different groups of diphenylpropane-based species is strongly influenced by the size and shape of zeolite void spaces, as was also corroborated by DFT calculation results. This allows nPB disproportionation to be quite useful for estimating the framework topology of zeolites with unknown structures, especially those of large-pore materials.

Zeolite-Catalyzed Disproportionation of iso-Propylbenzene: Identification of Reaction Intermediates and Mechanism

“…While the latter group of bicyclic aromatic compounds was found to be intermediates of iPB dehydrogenation, a side reaction of the iPB disproportionation, both groups of them are hardly observed over medium-pore zeolites, regardless of their structure type. However, we were not able to detect any di-iso-propylated 2,2-diphenylpropane (dipDP) species in this study, unlike the disproportionation of other aromatic hydrocarbons, including m-xylene, ethylbenzene, and n-propylbenzene, 12,17,18 in which formation of dialkylated diphenylalkane species as reaction intermediates has been clearly confirmed. To better understand the results described above, we have calculated the strain energies of three mipDP, three mip = DP, or six dipDP isomers embedded within the structures of zeolites studied, together with the relative energies of all species (i.e., reactant, reaction intermediates, transition states, and products) in the 84T H-Y model, using the mixed quantum-mechanical and semi-empirical ONIOM method.…”

“…The precise reason for this remains unknown, because di-n-propylated 1,1-diphenylpropane derivatives, the molecular dimensions of which cannot be smaller than those of dipDP species, can be formed within the supercages of H-Y during nPB disproportionation. 12 Figure 3 also shows that while the peak 5c due to one mipDP isomer is barely detectable from the cage-based, large-pore H-Y only, the peaks 4a,b and 5a,b assigned 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 to two of the three mip = DP and three mipDP isomers, respectively, are clearly visible from all four large-pore zeolites used in this study. This suggests that the shape-selective effects of large-pore zeolites are not strong enough to prevent the bimolecular iPB disproportionation, even over the 1D channel-based H-mordenite.…”

“…[4][5][6][7][8][9][10][11] One example is npropylbenzene (nPB) disproportionation, the detailed mechanism of which has remained until a very recent date. 12 A new bimolecular diphenylpropane (DPP)-mediated reaction pathway, in which both mono-and dipropylated DPP derivatives are serving as intermediates, has been proposed based on the ex situ gas chromatography-mass spectrometry (GC-MS) results from used zeolite catalysts. This reaction was also found to be useful for assessing the framework topology of large-pore zeolites, because the type of not only its main reaction intermediates but also that of side reaction ones formed during nPB disproportionation can differ notably according to the size and shape of zeolite void spaces.…”

TNU‐9 Zeolite: Aluminum Distribution and Extra‐Framework Sites of Divalent Cations

“…TNU-9 has been investigated as ac atalystf or both acid and redox reactions:T oluene [9b] and ethylbenzene [10] disproportionation, the methanol-to-hydrocarbons reaction (MTH), [11] the alkylationo fb enzene and toluene with methanol, ethanol, and isopropanol, [12] the isomerization and disproportionation of mxyleme, [9b, 13] the alkylation of benzene with n-hexane, [14] the hydroisomerization of n-hexane, [15] the alkylation of phenol with propylene, [16] and the disproportionation of n-propylbenzene [17] and isopropylbenzene [18] are examples of acid-catalyzed reactions that have been performed with the H-form of the TNU-9 zeolite.R edox-catalyzed reactions use transition-metal-exchanged TNU-9, for example, Co-TNU-9 and Cu-TNU-9, fort he selectivec atalytic reduction of NO, [19] and Cu-TNU-9 for the oxidation of propane. [20] Studies have shown that the TNU-9 zeolite represents ah ighly promising zeolite matrix for both acidand redox-catalyzed reactions.H owever,t he potential of this new zeolite cannot be fully evaluated without the knowledge of the aluminumo rganization in the TUN framework, which is not currently known.…”

“…TNU‐9 has been investigated as a catalyst for both acid and redox reactions: Toluene and ethylbenzene disproportionation, the methanol‐to‐hydrocarbons reaction (MTH), the alkylation of benzene and toluene with methanol, ethanol, and isopropanol, the isomerization and disproportionation of m ‐xyleme, the alkylation of benzene with n ‐hexane, the hydroisomerization of n ‐hexane, the alkylation of phenol with propylene, and the disproportionation of n ‐propylbenzene and isopropylbenzene are examples of acid‐catalyzed reactions that have been performed with the H‐form of the TNU‐9 zeolite. Redox‐catalyzed reactions use transition‐metal‐exchanged TNU‐9, for example, Co‐TNU‐9 and Cu‐TNU‐9, for the selective catalytic reduction of NO, and Cu‐TNU‐9 for the oxidation of propane .…”