HZSM-5 zeolite catalysts

Gayubo, A.G., Aguayo, A.T., Atutxa, A., Prieto, R., Bilbao, J., Deactivation of a HZSM-5 zeolite catalyst in the transformation of the aqueous fraction of biomass pyrolysis oil into hydrocarbons, Energy Fuels, 2004, 18, 1640. 

Zheng, S., Jentys, A., and Lercher, J.A. (2006) Xylene isomerization with surface-modified HZSM-5 zeolite catalysts an in situ IR study. ]. Catal, 241 (2), 304-311. 

Lee et al. (65) reported that the selectivity in connection with the formation of p-xylene from methanol and toluene can be improved significantly by adding Sb203 to the HZSM-5 zeolite catalyst. Without this additive, the xylene produced in the catalytic reaction of methanol and toluene over HZSM-5 at 400°C is an equilibrium mixture containing 23.1% p-xylene. However, the para selectivity approaches 100% if the reaction proceeds over the modified HZSM-5 catalyst prepared by calcining a mixture of HZSM-5 AND Sb203 in air at 500°C for 2 h. 

The cracking of PE/LCO and PP/LCO blends over HZSM-5 zeolite catalysts in the riser simulator at 450°C led towards mainly a C5-C12 hydrocarbon fraction of aromatic nature and a low yield of C1-C2 gases and coke. 

Activation and aromatization of methane and ethane over Mo(VI)/HZSM-5 and W(VI)/HZSM-5 zeolites catalysts... 

ZSM-5 zeolites have been widely used in selective conversion of hydrocarbons through various modification methods. It is well known that Zn- or Ga-containing ZSM-5 zeolites are excellent catalysts for C2-C4 paraffin aromatization called as Cyclar process. Moreover, light olefins of C2""-C4 can be produced from saturated hydrocarbons on modified ZSM-5 zeolite catalysts [1]. Lately a catalyst for CH4 aromatization, that can be regarded as an extension of the Cyclar process, has been derived from ZSM-5 zeolite modified with Mo(VI) species [2-3], In this presentation, the aromatization of CH4 and C2H6 over Mo(VI)/HZSM-5 and W( VI) /HZSM- 5 zeolite catalysts and their mechanistic features are investigated. 

The polarization of one C-H bond in CH4 and the formation of CH2 carbene over HZSM-5 will be much more difficult. However, the formation of CH2 can be promoted very much over Mo(Vl)/HZSM-5 zeolite catalysts since transition metal cations, such as Mo(Vl) in high valence state, will be more favorable for the polarization of C-H bond in... 

CH4 and the Mo=CH2 carbene species are more stable. The effect of Mo loading on the CH4 conversion over Mo(VI)/HZSM-5 zeolite catalyst is summarized in Table 1. From Table 1 we can see that the best Mo loading is about 2-3%. Further increase in Mo loading in Mo(VI)/HZSM-5 will lead to a remarked decrease in the CH4 conversion. Since only HZSM-5 zeolite is a good support for the reaction, the acidity and intermediate size pore structure of HZSM-5 are also vital to the aromatics formation. Table 2 summarized the results of the Mo loading on physical properties of ZSM-5 zeolite. 

This reaction may also be possible over the Mo(VI)/HZSM-5 zeolite catalyst. 

Recently, Weitkamp and coworkers[75] applied the CLD-modified HZSM-5 zeolite catalyst to the hydroconversion of methylcyclohexane (MCH) to obtain high-quality water vapor cracking feedstock that is, C2 normal alkanes. The modifying agent they used was Si(OC2H5)4 (TEOS), and the solvent was n-heptane. The preparation procedure is similar to that invented by Gao et al., and the reaction results are listed in Table 6.19. 

Table 6.19 Product distribution of methylcyclohexane hydroconversion over CLD-modified HZSM-5 zeolite catalyst (400°C)...

Pore size regulated ZnO-ZSM-5 zeolite enhanced the paraxylene concentration as high as 99% in the xylene fraction of the product in the aromatization of paraffinic C4-C6 hydrocarbon stream as against the unmodified HZSM-5 zeolite. The enhancement of paraxylene selectivity is a function of extent of silica deposition. However, the formation of other major products benzene and toluene does not get affected. The pore size regulated ZnO-HZSM-5 zeolite catalyst has got good potential for converting low value C4-C6 hydrocarbons to value added aromatics like benzene, toluene and paraxylene. 

HZSM-5 zeolite catalysts show high shape selectivity, because they have very fine micro pores within its crystallite [1], The pore diameter is almost equal to sizes of mono-aromatic molecules [2]. HZSM-5 catalysts are typical solid-acid catalysts, and their acid sites are distributed not only within but also on the outer surface of the crystallite [1,3]. Therefore, the shape selectivity of HZSM-5 zeolite is affected strongly by the size of the crystallite, the intracrystalline diffusivities of hydrocarbons and acidic properties within and on the outer surface of the crystallite [4-7],... 

Kinetic Modelling for Deactivation by Coke Deposition of a HZSM-5 Zeolite Catalyst in the Transformation of Aqueous Ethanol into Hydrocarbons... 

As biomaterials are structurally and chemically complex, biomass thermochemical conversion processes (1,2) produce complex fractions including a liquid fraction which, dep>ending on the process, can be obtained in large (liquefaction, pyrolysis) or small yields (gasification). These liquids have found little utility because of their large contents in oxygen which implies low heat values, instability and corrosive prop>erties. Two routes have been tested (3,4) in order to produce hydrocarbons from these liquids. The first one involves hydrotreatment with either H2 or H2 + CO over classical hydrotreatment catalysts. The second route is the simultaneous dehydration and decarboxylation over HZSM-5 zeolite catalyst in the absence of any reducing gas. 

Recent work at SERI has focussed on the study of direct wood-vapor conversion without an oil condensation step (J ). The MBMS experimental system (18-21) has been used to show that the biomass pyrolysis vapors were reactive on the HZSM-5 zeolite catalyst. The complete destruction of all primary products was observed, and a method of monitoring deactivation of the catalyst was demonstrated. Specifically, the carbohydrates were converted beyond the furans to light olefins and aromatics and the lignin products were also completely destroyed with the same classes of gaseous products. However, the coking tendency of each class of starting material was not quantified at that time. 

Zn/HZSM-5 catalysts known as efficient systems for ethane and propane aromatization (the UOP Cyclar Process) also showed some activity in methane aromatization [69]. At 723 K, methane can easily be activated in the presence of ethylene in the feed and converted to higher hydrocarbons (C -C ) and aromatics (Cg-C,g), through its reaction over rare metals modified Zn/HZSM-5 zeolite catalysts. The CH conversion of 37.3% was obtained and the catalysts showed a longer lifetime than usual metal supported HZSM-5 zeolite catalysts without adding any rare-earth metals. 

Gayubo AG, Aguayo AT, Atutxa A, Valle B, Bilbao J. Undesiied components in the transformation of biomass pyrolysis oil into hydrocarbons on an HZSM-5 zeolite catalyst J Chem Technol Biotechnol... 

Valle, B., et al., 2010. Selective production of aromatics by crude bio-oil valorization with a nickel-modified HZSM-5 zeolite catalyst. Energy Fuels 24 (3), 2060—2070. 

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