Improvement of catalyst

The procedure is technically feasible, but high recovery of unconverted raw materials is required for the route to be practical. Its development depends on the improvement of catalysts and separation methods and on the avaHabiUty of low cost acetic acid and formaldehyde. Both raw materials are dependent on ample supply of low cost methanol. 

Water injection in a dehydrogenation process Improvement of catalyst activity through water injection 84... 

Since plastomeric polypropylenes were insufficiently investigated, further improvement of catalyst activity correlated with an easy synthetic approach was required. Therefore, the two asymmetric hafnocene dichloride complexes, each bearing a 2,5,7- and 2,4,6-trimethyl substituted indenyl moiety (4a, 4b) were developed. 

Further improvement of catalyst 387 resulted in the development of catalyst 393, as demonstrated by the formation of 391 and 392 from dienophiles 390 and cyclic dienes which gave good results with less reactive dienes and dienophiles (equation 117, Table 21)245. 

The most successful New Demet preparation, A, showed a MAT conversion of 77.1% compared to 65.2% for the untreated equilibrium catalyst. This increase in conversion was accompanied by an increase in gasoline yield from 6.8 to 52.3% and a decrease in coke yield from. 5 to. 3%. These results were achieved by subjecting the catalyst to a series of treatments after the basic gas phase reactions, involving oxidative and reductive washes, and ion exchange with NHz + and RE (see Fig. 1). Each of these treatments resulted in a successive improvement of catalyst performance. 

Taken together, these results indicate that dehydrated cells could be an alternative catalyst for the conversion of poorly water-soluble compounds and that it might be possible to treat a mixture of pollutants by combining strains. Nevertheless, for future application the improvement of catalyst stability is still needed and is currently being studied. 

As it is clear that the higher the exchange current density, the lower the penetration depth and catalyst utilization, it is evident that for the more active platinum metal catalysts, an improvement of catalyst performance by using highly porous coatings is neither expected nor observed, as the normal coating roughness of 1 /im already corresponds to the penetration depth in a nanopore (82). 

Several patents were issued on this topic. For example, Rueter [34] in his patent cited about 120 US patents and about 40 foreign patents in the period 1987-2004. The actual number of patents is higher, but already these numbers indicate that many aspects of catalyst and process technology are covered. Patents in the last five years (2003-2008) were thus focused either on the improvement of catalyst preparation and/or improvement of reaction/reactor operations, particularly with strong attention on the safety of operations. However, often in the cited patents operations are still... 

Einaga H., Futamura S., Ibusuki T. (2001) Improvement of Catalyst Durability in Benzene Photooxidation by Rhodium Deposition on Ti02, Chem. Lett. 582-583. 

During induction, catalyst activity and selectivities to aromatics and propene increase steadily. Improvement of catalyst performance is due to increase in Ga dispersion and formation of dispersed Ga species (Gao) which are efficient for the heterolytic recombinative release of hydrogen [18,191. The Ga/H-MFI catalyst then reaches its optimal aromatisation performance (stabilisation). Ci to C3 hydrocarbons productions are at their lowest. The gallium dispersion and the chemical distribution of Ga are optimum and balance the acid function of the zeolite. Reversible deactivation during induction and stabilisation of the catalyst is due to site coverage and limited pore blockage by coke deposition. 

This chapter is concerned with the improvement of catalyst performance through a better pellet design. This design relates to the physical properties of the catalyst pellets for given kinetics and does not involve the chemical composition of the catalyst. Examples are given to illustrate the influence of structural parameters on catalyst performance. 

With the improvement of catalyst, the activity of many synthesis reactions has been increased. This leads to a change in reactors from traditional fluidized bed or packed bed to FFB for better reaction selectivity and high throughput. A comparison of selectivity for various reactors is shown in the table. 

Figure 7 shows an improvement of catalyst stability after the stabilization treatment. This clearly indicates that modification of acidity by steaming can enhance the stability of HZSM-5. The coke deposited on the catalysts were analyzed and divided by the total number of acid sites determined by ammonia TPD. It was expressed as the amount of coke per number of acid site and the result is shown in Figure 8. The figure demonstrates that there is no change in the amount of coke produced by the acid site after the stabilization treatment. This may suggest the nature of coke-forming sites for both stabilized and unstabilized catalysts are identical. Therefore we do not expect predominant passivation of some of the acid sites with certain strength and nature.

Development of the microspherical catalyst in 1946, from Al203-Si02 sol by means of spray drying, contributed to major advances in fluidized catalyst-bed technology, especially for improvement of catalyst fluidity, decrease of attrition loss, and decrease of erosion in transfer lines. 

An improvement of catalyst activity, especially for the oxidation of electron-poor, deactivated systems like p-toluic acid, can be reached by addition of other transition metal compounds to the Co/Mn/Br catalyst. The most prominent additive is zirconium(IV) acetate, which by itself is totally inactive. An addition of zirconi-um(IV) acetate (ca. 15 % of the amount of cobalt) can yield reaction rates which are higher than those observed using a tenfold amount of cobalt acetate. This amazing co-catalytic effect can be attributed to the common ability of zirconium to attain greater than sixfold coordination in solution, to the high stability of Zr toward reduction, and to the ability of zirconium or Hf to redistribute the dimer/ monomer equilibrium of dimerized cobalt acetates (Co 7Co, Co VCo " systems) by forming a weak complex with the catalytically more active monomeric Co species [17]. 

While the molecular tantalum catalyst Ta(OCH2CH3)5 exhibited very poor activity for epoxidation under Sharpless conditions, the surface-supported analogue [a mixture of 70% =SiOTa(OCH2CH3)4 and 30% (=SiO)2Ta(OCH2CH3)3] was shown to have activity comparable with that of the molecular Ti catalyst. Furthermore, excellent enantiomeric ee values (up to 94%, compared with 96 % for Ti[OCH(CH3)2]4 under the same conditions) were obtained. An inversion of the the major enantiomer obtained was observed for both the molecular and supported tantalum catalysts, i. e., the association of tetraisopropyltitanium and (+)-diisopropyltartrate produces (/f)-epoxide whereas the Ti catalyst with (+)-diisopropyltartrate produces the (S)-epoxide. The putative active species, =SiOTa(OCH2CH3)2[(+)-(DET)] (Structure 18) has also been synthesized and tested (eq. (3) [23 a]) Further improvements of catalyst activity have been obtained by modification of the support and refinement of the synthesis of the supported tantalum alkoxide precursor. 

Currently, there are four major lines of research in the gas-phase epoxidation of propylene (1) mechanistic studies of Au/Ti02 catalysts through kinetics, spectroscopic identification of adsorbed species, and surface science, (2) experimental and theoretical investigation of Au/TS-1 catalysts, (3) improvement of catalyst life of Au/3D mesoporous Ti-Si02 catalysts, and (4) replacement of Au with Ag on TS-1 supports. 

An important example of this kind is a contribution of cracking processes to partial oxidation of propane and higher hydrocarbons. In particular, in the case of catalytic propane ODH, the formation of lower hydrocarbons—first of all ethylene and methane—can substantially reduce propylene selectivity. The analysis of possible homogeneous and heterogeneous pathways of C-C bond breaking can provide valuable guidelines for further improvement of catalyst formulation and/or overall process design. 

The research programs resulted in the development of novel preparation techniques for exhaust catalysts, which led to a general improvement of catalyst performance. Besides the enhancement in activity the new preparation techniques make it possible to be more flexible and prepare tailor-made catalysts. 

The purification of the exhaust gas of PTA plants is one application where halohydrocarbon destruction catalysts have found use at a global scale (12, 13, 17, 18). Typically the untreated exhaust contains a mixture of volatile organic components including methyl bromide, carbon monoxide, hydrocarbons, methyl acetate, and organic acids. The presence of the methyl bromide sets forth the requirement that a catalyst such as the HDC be used. Additionally, the catalyst must be able to effectively destroy all the other organic components (with their widely different intrinsic reactivities toward air oxidation) of the mixture at reasonably low temperatures. Currently most PTA offgas remediation catalysts are used at an inlet temperature higher than 350°C. An improvement of catalyst activity is desired to... 

Catalysis, an important scientific and technological area for the development of environmentally friendly chemical processes, which m turn form the basis for cleaner industnal development and are also the key elements for an industrial prevention approach New, less polluting processes together with the optimization of existing processes depend to a great extent on the improvement of catalyst performance m the heavy and fine chemical production lines with a direct impact on the quality and quantity of by-products or waste generated... 

Further improvements of catalysts activities are still possible by carefully controling the interactions between active phase precursors and supports. This has been done through introduction of complexing agents [8] as well as the use of new supports such as silica, titanium oxide or carbon. However, easily obtaining promoted catalysts on those supports is still topical issue. 

Hydroformylation catalysts typically consist of a transition-metal atom (M) to form metal carbonyl hydride species. In some cases, these complexes are modified by additional ligands (L). The general structure is H cM3,(CO)zL . This type of active hydroformylation species may be generated by precursors of different composition. Since the catalytic activity and selectivity are closely related to the metal atom and ligands, the improvement of catalyst performance can mainly be achieved by the variation of the center atom or the modification of the ligands [44,45]. 

In order to enhance space-time yields of catalytic gas-phase reactions, two strategies are in principle possible the improvement of catalyst activity or the implementation of more intense process conditions. This usually leads to an increase of heat production that can only be partially released, if at all, using conventional reactor technology. 

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