Zeolite gallium-modified

The aromatization of liquefied petroleum gases (LPG) has been investigated for more than a decade due to its economical and strategic importance for the exploitation of natural gas reserves and valorization of light hydrocarbons obtained from petroleum refining. Commercially, these reactions using gallium modified ZSM-5 zeolite catalysts are known as Cyclar process, developed jointly by UOP and BP [1]. 

The gallium modified zeolites were activated by two successive reduction-oxidation cycles, respectively with hydrogen and air, which, according to the literature [3], lead the catalyst to its most active form. 

In contrast, an extremely low activity was observed for the gallium-modified silicalite-1. scrambling started first at 723 K, which clearly indicates that Bronsted acid sites are necessary to activate propane adsorbed on zeolites Ga/ HZSM-5 179,181. A low activity was also observed for C-2-propane adsorbed on zeolite HZSM-5 in the absence of gallium. On this catalyst, C scrambling was observed after heating at 573 K for 20 min, and the theoretical 2 1 ratio of the signal intensities of methyl and methylene groups was reached after 80 min at 573 K. 

One process that occurs by these mechanisms, called the Cyclar process, uses a gallium-modified zeolite catalyst. The gallium increases the rate of the early cracking steps that generate alkenes. The Cyclar process can convert butane, propane, and ethane to mixtures of benzene, toluene, and the isomeric xylenes. The reactivity order is butane > propane > ethane. 

Figure 1.21 Process flow diagram for the conversion of light alkanes and alkenes to benzene, toluene, and xylene catalyzed by a gallium-modified zeolite (UOP-BP Cyclar process). Adapted from Ref. (303).

Recent advances have shown zeolites are effective in catalysing the direct conversion of synthesis gas to motor fuels. The MTO (methanol-to-olefins) process converts MeOH to C2-C4 alkenes and is also catalysed by ZSM-5. The development of a gallium-modified ZSM-5 catalyst (Ga-ZSM-5) has provided an efficient catalyst for the production of aromatic compounds from mixtures of C3 and C4 alkanes (commonly labelled LPG). 

Dapsens PY, Kusema BT, Mondelli C, Perez-Ramirez J (2013) Gallium-modified zeolites for the selective conversion of bio-based dihydroxyacetone into C1-C4 alkyl lactates. J Mol Catal A Chem. http //dx.doi.Org/10.1016/j.molcata.2013.09.032... 

The isomorphous replacement of aluminum by gallium in the framework structure of zeolites (beta, MFI, offretite, faujasite) offers new opportunities for modified acidity and subsequently modified catalytic activity such as enhanced selectivity toward aromatic hydrocarbons [249,250]. The Ga + ions in zeolites can occupy tetrahedral framework sites (T) and nonframework cationic positions. 

One Interesting and industrially important process developed recently,"the cyclar process" is the catalytic aromatization of light (C3-C5) hydrocarbons over pentasil based catalysts. These new classes of solids have been widely studied (1-9). These Investigations led to the conclusion that the catalysts consisting of gallium, zinc, Pt, and modified H-ZSM-5 were more active and more selective towards aromatics than the parent H-ZSM-5 zeolite. The formation of aromatics from light alkanes comprised several main hydrocarbon reactions alkane... 

A completely new approach for BTX production has emerged in recent years. It converts C2 to C6 paraffins into aromatics using a modified ZSM-5 zeolite catalyst which contains gallium (19). An example of this approach, the Cydar process, has been in commercial operation by British Petroleum at Grangemouth, Scodand since August 1990 (20). It uses C3 C4 feed and employs UOP s CCR technology to compensate for rapid catalyst coking. 

Choudhary, V. R., Jana, S. K., Patil, N. S., Bhargava, S.K. Friedel-Crafts type benzylation and benzoylation of aromatic compounds over I l/i zeolite modified by oxides or chlorides of gallium and indium. Microporous Mesoporous Mater., 2003, 57, 21-35. 

Two medium-pore zeolites, namely, ferrierite (Si/Al = 6.3) and theta-1 (Si/Al = 30) were used in this work. They were used as catalysts in the H-form or were modified by gallium before catalytic experiments. In the latter case, Ga was introduced into the zeolites by an incipient wetness impregnation method, using aqueous solutions of Ga(N03)3. In this work, catalysts with a Ga content of 2.2 wt.% were investigated. 

The aromatization of butane on zinc modified HZSM-S and gallium-and/or copper-modified HZSM-5 was studied. The activity, selectivity and thermal stability of the Zinc-modified catalysts prepared by various methods were discussed. The zinc loaded on HZSM-5 by the impregnation showed the highest activity. However, at a reaction temperature higher than 873K this catalyst lost part of the zinc fi om the zeolite surface. On the other hand, the zinc loaded into the zeolite firamework showed relatively low activity and selectivity to aromatics donation, but it showed relatively high thermal stability. 

There is considerable interest in isomorphous substitution of aluminium in the zeolite framework by other elements and some papers have described the synthesis of MFI zeolites containing boron, gallium, titanium and iron as lattice elements (ref.1-3). The replacement of Al ions with the ions of another element can modify both the acidity and pore size features of the zeolite (ref.4, 5), resulting in modification of the catalytic property of zeolite catalysts (ref.6-8). 

The catalyst in MOI contains only ZSM-5 and/or ZSM-11 without any large pore zeolites. The ZSM-5 and/or ZSM- 11 preferably have a high initial silica/aliunina molar ratio and are modified by phosphorus and metals such as gallium. 

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