Functionalization catalysts

Historically, the isomerization catalysts have included amorphous siUca-aluminas, zeoHtes, and metal-loaded oxides. AH of the catalysts contain acidity, which isomerizes the xylenes and if strong enough can also crack the EB and xylenes to benzene and toluene. Dual functional catalysts additionally contain a metal that is capable of converting EB to xylenes. 

Commercial processes which use a dual-functional catalyst are Octafining, Isomar, and Isolene. 

UOP s Isomar process (56,117—119) was originally developed to use dual-functional catalysts. The first-generation catalyst contained Pt and halogen on alumina. Operating conditions using this catalyst were 399°C 1.25 MPa 2 LHSV and H2/hydrocarbon ratio of 6 1. A Cg naphthene concentration of... 

One system for measuring catalyst failure is based on two oxygen sensors, one located in the normal control location, the other downstream of the catalyst (102,103). The second O2 sensor indicates relative catalyst performance by measuring the abiUty to respond to a change in air/fuel mixture. Other techniques using temperatures sensors have also been described (104—107). Whereas the dual O2 sensor method is likely to be used initially, a criticism of the two O2 sensors system has been reported (44) showing that properly functioning catalysts would be detected as a failure by the method. 

Powerforming is basically a conversion process in which catalytically promoted chemical reactions convert low octane feed components into high octane products. The key to a good reforming process is a highly selective dual-function catalyst. The dual nature of this catalyst relates to the two separate catalyst functions atomically dispersed platinum to provide... 

The biradical catalysts described previously for double-base propints (Ref 80) are also effective for hydrocarbon propints. Table 34 shows how p,p,-biphenylene-bis(diphenylmethyl) compares to n butyl ferrocene as a catalyst in a carboxy-terminated polybutadiene. These catalysts are claimed to overcome all of the processing difficulties, chemical stability and volatility disadvantages attributed to catalysts based on ferrocene and carborane derivatives. Another somewhat similar functioning catalyst, the free radical compd, 2,2-diphenylpicrylhydrazyl,... 

Bioconjugates of Compatible Enzymes as Functional Catalysts for Multistep Processes... 

Abstract A three-function catalyst model for hydrocarbon SCR of NOx is described, based on experimental evidence for each function, during temperature-programmed surface reactions (TPSR). 

Keywords Three-function catalyst oxygenates dinitrogen formation supported homogeneous catalysis metal cation active sites. 

The complete CAT I, three-function catalyst - CoPd/HMOR -(Figure 5.3)... 

NO dissociation to N2, during TPD of NO pre-adsorbed at RT on the active site of the third function catalyst supported Co2+ on HMOR (Cat III, function 3 alone) selected for the sake of demonstration [12]... 

The temperature of DeNOx reaction (function 3) comparing Figure 5.5a (NO TPD, Cat nr) to Figure 5.5b - TPSR in the presence of a three-function catalyst (CoPd/HMordenite, Cat I ), in a complete flowing feed N0/HC(CH4)/02 (excess) -the temperature of DcNOx is that of the NO thermal desorption. According to the model, the catalyst will have to produce C H O . (CH3OH, HCHO) (function 2) to proceed to the DcNOx process, as discussed in Section 4.2. 

Case of CoPd/HMOR (three-function catalyst Cat V) [12]... 

The CoPd/HMOR three-function catalyst is able to produce by itself mild oxygenates of methane, CH3OH and HCHO, above 100°C (373 K), as seen in Figure 5.6. It can be... 

The design of a three-function catalyst, for a given application with specific reductants, will be easier in the framework of the model. 

Chiral recognition of A-[Co(phen)3]3+ has been observed in a modified /3-cyclodextrin.772 Chiral discrimination has also been seen in photoinduced energy transfer from luminescent chiral lanthanoid complexes773 to [Co(phen)3]3+ and between photoexcited [Ru(bpy)3]2+ and [Co(phen)3]3+ co-adsorbed on smectite clays.774 The [Co(bpy)3]3+ ion has been incorporated into clays to generate ordered assemblies and also functional catalysts. When adsorbed onto hectorite, [Co(bpy)3]3+ catalyzes the reduction of nitrobenzene to aniline.775 The ability of [Co(phen)3]3+ to bind to DNA has been intensively studied, and discussion of this feature is deferred until Section 6.1.3.1.4. 

Hydrogen oxidation can be done in situ, using a bi-functional catalyst (6—11), or the two processes can be separated by feeding the dehydrogenation... 

In many cases there is an interaction between the carrier and the active component of the catalyst so that the character of the active surface will change. For example, the electronic character of the supported catalyst may be influenced by the transfer of electrons across the catalyst-carrier interface. In some cases the carrier itself has a catalytic activity for the primary reaction, an intermediate reaction, or a subsequent reaction, and a dual-function catalyst is thereby obtained. Materials of this type are widely employed in reforming processes. There are other cases where the interaction of the catalyst and support are much more subtle and difficult to label. For example, the crystal size and structure of supported metal catalysts as well as the manner in which the metal is dispersed can be influenced by the nature of the support material. 

In the reverse flow type, the hydrotreater reactor is fed with fresh and recycled feeds, and is operated to accomplish partial conversion of that combined feed in the first stage. A graded HDT-HCK bed or a multi-functional catalyst can be used in the first stage. A very effective H2 separation is used for the first-stage effluent gas. A bottoms fractionator or an adsorption unit is used for removal of heavy PAHs. Carbon adsorption extends the catalyst life. The liquid product of the first reactor is mixed with a mixture of fresh and recycled H2. The whole second stage effluent is hydrotreated in the first stage. 

Butamer [Butane isomerization] A process for converting n-butane into iso-butane conducted in the presence of hydrogen over a dual-functional catalyst containing a noble metal. Developed by UOP and licensed worldwide since 1959. In 1992, more than 55 units had been licensed. 

Production of p-xylene via p-xylene removal, i.e., by crystallization or adsorption, and re-equilibration of the para-depleted stream requires recycle operation. Ethylbenzene in the feed must therefore be converted to lower or higher boiling products during the xylene isomerization step, otherwise it would build up in the recycle stream. With dual-functional catalysts, ethylbenzene is converted partly to xylenes and is partly hydrocracked. With mono-functional acid ZSM-5, ethylbenzene is converted at low temperature via transalkylation, and at higher temperature via transalkylation and dealkylation. In both cases, benzene of nitration grade purity is produced as a valuable by-product. 

In a laboratory scale dehydrocyclization reaction using a dual-function catalyst, Davis (8) reported that the aromatic products were o-xylene, /w-xylene and ethylbenzene in approximately equal amounts (ca. 20-30% each) and p-xylene (ca, 15%). The formation of these was assumed to be from a direct 1,6-ring closure, as sketched in the following two diagrams ... 

As previously mentioned, Davis (8) has shown that in model dehydrocyclization reactions with a dual function catalyst and an n-octane feedstock, isomerization of the hydrocarbon to 2-and 3-methylheptane is faster than the dehydrocyclization reaction. Although competitive isomerization of an alkane feedstock is commonly observed in model studies using monofunctional (Pt) catalysts, some of the alkanes produced can be rationalized as products of the hydrogenolysis of substituted cyclopentanes, which in turn can be formed on platinum surfaces via free radical-like mechanisms. However, the 2- and 3-methylheptane isomers (out of a total of 18 possible C8Hi8 isomers) observed with dual function catalysts are those expected from the rearrangement of n-octane via carbocation intermediates. Such acid-catalyzed isomerizations are widely acknowledged to occur via a protonated cyclopropane structure (25, 28), in this case one derived from the 2-octyl cation, which can then be the precursor... 

As mentioned, cyclopentanes can be formed with monofunctional catalysts, and so even with dual function catalysts, one would expect some of the cyclopentanes to form via mechanisms associated with the platinum reactivity part of the dual functionality. 

While a majority of laboratory-scale dehydrocyclization studies involve carefully chosen feedstocks, often a single alkane, commercial operators use a naphtha fraction consisting of a complex mixture of hydrocarbons. At least some of these will be incapable of easily undergoing direct dehydrocyclization and need to be isomerized into reactive structures if aromatics are to be formed. The work of Davis suggests that the acidity of dual function catalysts is an important added factor in these isomerizations, one which likely complements the different set of isomerizations that may be catalyzed by the platinum function. 

Although there is clear experimental evidence (8) in model dehydrocyclization reactions, using a dual function catalyst, that carbocations are... 

In contrast to this mechanism, the one proposed in our work operates direct from the oxidation state of the alkane feedstock. The same alkyl cation intermediate can lead to both alkane isomerization (an alkyl cation is widely accepted as the reactive intermediate in these reactions) and we have shown in this paper that a mechanistically viable dehydrocyclization route is feasible starting with the identical cation. Furthermore, the relative calculated barrier for each of the above processes is in accord with the experimental finding of Davis, i.e. that isomerization of a pure alkane feedstock, n-octane, with a dual function catalyst (carbocation intermediate) leads to an equilibration with isooctanes at a faster rate than the dehydrocyclization reaction of these octane isomers (8). 

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