Surface species formed during propane aromatization over Zn/MFI catalyst as determined by in situ spectroscopic techniques

Ivanova, I. I.; Kolyagin, Yu. G.; Ordomsky, Vitaly V.; Asachenko, Ekaterina V.; Pasynkova, E. M.; Pirogov, Yu. A.

doi:10.1016/j.molcata.2008.10.051

Cited by 59 publications

(105 citation statements)

References 63 publications

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“…Interestingly, a significant absorbance at 1560 cm −1 could be seen over Zn 0.51 /Z950. This absorbance could most likely be attributed to olefins with internal double bond, polyenic species or precursors of aromatic compounds [38,39]. The effluent Catalysts 2019, 9, 100 9 of 15 of DB-FTIR cell reactor was monitored by mass spectrometer (Figure 11), Zn 0.51 /Z950 generates a higher amount of olefins and aromatics than Zn 0.50 /Z950R, which indicates that Zn species located in hydroxyl nests obtained better dehydrogenative aromatization performance than Zn species located in Si(OH)Al groups.…”

Section: Catalytic Performance Of Zn Species Located In Hydroxyl Nestmentioning

confidence: 99%

Operando Dual Beam FTIR Study of Hydroxyl Groups and Zn Species over Defective HZSM-5 Zeolite Supported Zinc Catalysts

Lin

Zhang

et al. 2019

Catalysts

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A series of defective ZSM-5 zeolites (~300 nm, SiO 2 /Al 2 O 3 ratio of 55, 100, 480 and 950) were systematically studied by XRD, SEM,29 Si MAS NMR, argon physisorption, NH 3 -TPD and FT-IR technologies. The nature, the amount and the accessibility of the acid sites of defective ZSM-5 zeolites are greatly different from reported ZSM-5 zeolites with a perfect crystal structure. The Brønsted acid sites (Si(OH)Al) with strong acid strength and the Brønsted acid sites (hydroxyl nests) with weak acid strength co-existed over defective ZSM-5 zeolites, which leads to a unique catalytic function. Zn(C 2 H 5 ) 2 was grafted onto defective ZSM-5 zeolites through the chemical liquid deposition (CLD) method. Interestingly, FT-IR spectroscopic studies found that Zn(C 2 H 5 ) 2 was preferentially grafted on the hydroxyl nests with weak acid strength rather than the Si(OH)Al groups with strong acid strength over different defective ZSM-5 zeolites. In particular, home-built operando dual beam FTIR-MS was applied to study the catalytic performance of Zn species located in different sites of defective ZSM-5 zeolites under real n-hexane transformation conditions. Results show that Zn species grafted over hydroxyl nests obtain better dehydrogenative aromatization performance than Zn species over Si(OH)Al groups. This study provides guidance for the rational design of highly efficient alkane dehydrogenative aromatization catalysts.Catalysts 2019, 9, 100 2 of 15 hydroxyl nests obtain very weak acidity, which is suitable for special applications [7]. For example, Beckman rearrangement reaction (cyclohexanone oxime to form ε-caprolactam in gas phase at 350 • C) could be catalyzed by the hydroxyl nests over silicalite-1 with high activity and selectivity [8]. Besides providing weak acidity, the hydroxyl nests could also provide active sites and space for the grafting of heteroatoms such as Sn, Ti and B, etc. [9]. As is well known, the preparation of heteroatom substituted silica-alumina zeolites through direct synthesis occurs at low efficiency, such as in the case of the preparation of Sn-Beta and TS-1 [10,11]. The preparation procedure is usually complex and needs to be controlled strictly. In comparison, grafting heteroatoms over hydroxyl nests by post-treatment could be operated at much milder conditions.The special property of hydroxyl nests has been known for decades, however, the application of them has only been restricted in the Beckmann rearrangement. Jia et al. reported that the hydroxyl nests are responsible for the rapid deactivation of ZSM-5 zeolite in methanol conversion [12]. The hydroxyl nests accelerate the secondary reaction and coke formation side-reactions [13]. HZSM-5 zeolite with MFI structure (0.55×0.55 nm zigzag, 0.55×0.57 nm straight channel) [14] has been widely applied in many heterogeneous catalytic processes [15]. The well-developed porous structure with a high surface area and strong acidity endows the extraordinary performance of HZSM-5 as a successful solid acid catalyst. The acidity of HZSM-5 originates ...

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Section: Catalytic Performance Of Zn Species Located In Hydroxyl Nestmentioning

confidence: 99%

Operando Dual Beam FTIR Study of Hydroxyl Groups and Zn Species over Defective HZSM-5 Zeolite Supported Zinc Catalysts

Lin

Zhang

et al. 2019

Catalysts

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“…Various metal oxides supported zeolite have been widely investigated for light alkane (i.e., methane, ethane, propane) conversion, including precious metal Pt [18,19] and transition metal Zn [20][21][22][23][24][25], Ga [26][27][28][29][30], Mo [31,32], Co [33], Zr [34][35][36] oxides, etc. Moreover, metal modification also has a potential effect on the acidity of ZSM-5.…”

Section: Introductionmentioning

confidence: 99%

Relationship between Acidity and Activity on Propane Conversion over Metal-Modified HZSM-5 Catalysts

Zhou

Zhang

et al. 2021

Catalysts

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A systematic study of the comparative performances of different metal-impregnated HZSM-5 catalysts (Zn, Ga, Mo, Co, and Zr) for propane conversion is presented. The physicochemical properties of catalysts were characterized by means of XRD, BET, SEM, TEM, FTIR, XPS, 27Al MAS NMR, NH3-TPD and Py-FTIR. It was found that the acidities of the catalysts were significantly influenced by loading metal. More specifically, Mo-, Co- or Zr-modified catalysts showed a large metal size and low acidic density, resulting high olefin selectivity, while Zn- or Ga-modified catalysts maintained their small metal size and acidic density, and mainly reduced B/L due to the Lewis acid sites created by Zn or Ga species, resulting in high aromatics selectivity. Experimental results also showed that there is a balance between metals size and medium and strong acidity on propane conversion. Moreover, based on the different acidity of metal-modified HZSM-5 catalysts, the mechanism of propane conversion was also discussed.

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“…An increase in the reaction temperature led to the disappearance of the signals at δ ≈77.4 ppm and then at δ ≈68.1 ppm and the appearance of peaks in the spectral regions of δ =20–30 and 120–140 ppm corresponding to saturated and unsaturated carbon atoms of branched olefins and polyenic species 15. 18 Thus, the initially formed surface alkoxides and ethers are decomposed into alkenes, which undergo further reactions that lead to long‐chain oligomeric carbonaceous deposits.…”

Section: Methodsmentioning

confidence: 99%

Catalysis by Coke Deposits: Synthesis of Isoprene over Solid Catalysts

2013

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Nützlicher „Abfall“: Kohlenstoffhaltige Ablagerungen spielen eine zentrale Rolle bei der selektiven heterogenkatalytischen Synthese von Isopren aus Formaldehyd und Isobuten. Sie reichern sich während der Induktionsperiode an der Katalysatoroberfläche an und fördern die Wechselwirkung der Substrate im stationären Zustand. Der postulierte Mechanismus (siehe Schema) dient als Ansatzpunkt für den gezielten Entwurf fester Katalysatoren für die Isoprensynthese.

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Surface species formed during propane aromatization over Zn/MFI catalyst as determined by in situ spectroscopic techniques

Cited by 59 publications

References 63 publications

Operando Dual Beam FTIR Study of Hydroxyl Groups and Zn Species over Defective HZSM-5 Zeolite Supported Zinc Catalysts

Operando Dual Beam FTIR Study of Hydroxyl Groups and Zn Species over Defective HZSM-5 Zeolite Supported Zinc Catalysts

Relationship between Acidity and Activity on Propane Conversion over Metal-Modified HZSM-5 Catalysts

Catalysis by Coke Deposits: Synthesis of Isoprene over Solid Catalysts

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