Improvement of catalyst performance

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. 

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). 

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. 

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. 

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... 

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]. 

Other preparation steps, such as loading the support with Pd and Au, washing, drying, reducing and promoting with potassium acetate, have also been optimized to contribute to the improvement of catalyst performance. The catalysts prepared by this modified method have a uniform distribution of highly dispersed Pd and Au... 

Catalysis and sustainable chemistry, for cleaner industrial production as process optimisation depend to a great extent upon the improvement of catalyst performance in bulk and fine chemical production. 

Performance Evaluation. Successful catalyst development requires a satisfactory means to determine the performance of the catalyst. The only significant proof of improvement in catalyst performance Hes in evaluation in a reactor under the proper conditions. 

ActivatedL yer Loss. Loss of the catalytic layer is the third method of deactivation. Attrition, erosion, or loss of adhesion and exfoHation of the active catalytic layer aU. result in loss of catalyst performance. The monolithic honeycomb catalyst is designed to be resistant to aU. of these mechanisms. There is some erosion of the inlet edge of the cells at the entrance to the monolithic honeycomb, but this loss is minor. The peUetted catalyst is more susceptible to attrition losses because the pellets in the catalytic bed mb against each other. Improvements in the design of the peUetted converter, the surface hardness of the peUets, and the depth of the active layer of the peUets also minimise loss of catalyst performance from attrition in that converter. 

Improve Chemical Engineering. Improvements in catalyst performance inevitably mean that the optimum plant operating condition will be different from that for the unimproved catalyst. Design changes may be needed to obtain the maximum benefit from improved performance. The cost of such changes must be taken into account when assessing the value of catalyst improvement. 

Since the discovery of the catalyst of Au over Ti02 support for vapor phase C3H6 epoxidation [1], great efforts have been made to understand the reaction mechanism in order to improve the catalyst performance [2,3]. Currraitly the Au catalyst suffers from low activity and fast deactivation, and is thus far from commercialization. Perhaps it is why at present no publication on the reaction kinetics can be found in the literature. 

Depending on the process conditions, different profiles of the active phase over the particle will be obtained. A completely uniform distribution of the active material over the particle is not always the optimum profile for impregnated catalysts. It is possible to purposely generate profiles in order to improve the catalyst performance. Fig. 3.28 shows four major types of active phase distribution in catalyst spheres. 

Since the initial work of Onto et al. (1) a considerable amount of work has been performed to improve our understanding of the enantioselective hydrogenation of activated ketones over cinchona-modified Pt/Al203 (2, 3). Moderate to low dispersed Pt on alumina catalysts have been described as the catalysts of choice and pre-reducing them in hydrogen at 300-400°C typically improves their performance (3, 4). Recent studies have questioned the need for moderate to low dispersed Pt, since colloidal catalysts with Pt crystal sizes of <2 nm have also been found to be effective (3). A key role is ascribed to the effects of the catalyst support structure and the presence of reducible residues on the catalytic surface. Support structures that avoid mass transfer limitations and the removal of reducible residues obviously improve the catalyst performance. This work shows that creating a catalyst on an open porous support without a large concentration of reducible residues on the Pt surface not only leads to enhanced activity and ee, but also reduces the need for the pretreatment step. One factor... 

Catalysts are heterogeneous sulfided nickel (or cobalt) molybdenum compounds on a y-alumina. The reaction has been extensively studied with substrates such as thiophene (Figure 2.40) as the model compound mainly with the aims of improving the catalyst performance. The mechanism on the molecular level has not been established. In recent years the reaction has also attracted the interest of organometallic chemists who have tried to contribute to the mechanism by studying the reactions of organometallic complexes with thiophene [41], Many possible co-ordination modes for thiophene have been described. 

A similar mechanism to the previous ones was proposed by Deng, Shi and coworkers for the bis(2-oxo-3-oxazolidinyl)phosphinic chloride (BOP-Cl, 269) catalytic Beckmann rearrangement (equation 82). Addition of the Lewis acid zinc chloride improved the catalyst performance and amides were synthesized in excellent yields (92-99%). 

A Rh on Si02 catalyst promoted with V and Sm showed similar improvements in catalyst performance.522 Sm3+ ions improve the dispersion of Rh and increase CO and H2 uptakes, enhancing the formation of acetaldehyde and acetic acid. Lower-valence V ions have a good H2 storage capacity, thereby increasing the hydrogenation ability of the catalyst and promoting the formation of ethanol. 

Rb+- and Cs+-impregnated X zeolites were found to exhibit the highest activity and selectivity in these transformations. A CsX zeolite treated with boric acid, for example, gave better than 50% overall selectivity in the formation of styrene and ethylbenzene (410°C, 60% conversion).275 Treatment of these catalysts with copper or silver nitrate resulted in further improvements in catalyst performance.276 The promoting role of these metals was suggested to be their involvement in dehydrogenation of methyl alcohol. 

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