Catalysis Letters

Mendioroz, S.

2004 Catalysis Letters

doi: 10.1007/BF00811766

Delmon, Bernard

2004 Catalysis Letters

doi: 10.1007/BF00811767

The petroleum industry gets confronted with more stringent requirements with respect to transportation fuels: diminution by a factor of 10, or more, of the sulphur content, and a drastic diminution of the aromatic content. Besides, the quality of the crude oil supply keeps diminishing on an average. For this, the hydrotreating processes (HDS, HDN, HDM, hydrogenation, hydrocracking) will occupy a still increasing place in the refining processes. In a first part, we shall select some of the most important results published recently: use of new modifiers and supports (TiO2, ZrO2, mixed oxides), of metals not yet used in hydrotreating (Ru, Rh, Pd, Pt, possibly Nb, associations RuU, PdU, VU etc.), confirmation of the existence of distinct catalytic sites (hydrogenation and hydrogenolysis of the heteroatom-carbon bonds). Other new results should contribute to clarify the controversies and uncertainties concerning the origin of synergy between different elements and the changes of selectivity as a function of the experimental conditions. For this last topic, reference shall be made to the CoMoS model and the remote control theory. In a second part, we shall summarise the new constraints that the hydrotreating processes will face. It will be necessary to save still more energy. It will also be necessary to achieve a better balance of the various reactions taking place in a given process. The overall selectivity of catalysts and processes will have to be improved. In the third part, we shall try to emphasize directions of research which could help reach the objectives. We shall shortly outline the future contributions of chemical engineering. We shall examine with more details the problems concerning the genesis of adequate catalytic sites (underlining the enormous influence of the activation steps) and the modification of activity by means of the composition of the reacting medium. As the problem of synergy remains crucial for the future developments, we shall also present results with new synergetic systems (WS2 + supported Rh or Pd; MoS2 + supported Pt). The new results give hope that the mechanisms of synergy could get clarified in the near future.

Corma, Avelino

2004 Catalysis Letters

doi: 10.1007/BF00811768

Catalytic processes on zeolites and catalytic characteristics of zeolites have been reviewed in the area of petrochemistry and refining.

Centi, G.

2004 Catalysis Letters

doi: 10.1007/BF00811769

Some aspects of the reactivity of vanadyl pyrophosphate catalysts inn-butane andn-pentane oxidation and propane ammoxidation are discussed in order to illustrate differences and peculiarities of the catalysts for the selective oxidation of alkanes in comparison to the catalysts for the selective oxidation of alkenes. The formation of alkenes as reaction intermediates, the catalytic and mechanistic differences in alkane and alkene conversion, their different effects in changing the active surface configuration, the relationship between surface concentration of adspecies and catalytic behavior, and the problem of the surface isolation of the active intermediates are discussed. Some brief economic considerations about the advantages of the various processes of alkane oxidation as compared to alkene or aromatic oxidation are also given.

Fierro, J.

2004 Catalysis Letters

doi: 10.1007/BF00811770

This work summarizes the most relevant facets of the current knowledge of the principal catalytic processes involved in one carbon-atom conversions. Without doubt, natural gas (or methane) chemical conversion into high molecular weight hydrocarbons via oxidative coupling (OCM) or partial oxidation into C1 oxygenates (POM) currently represents a great chemical and technological challenge for petrochemistry. Although the catalyst systems and the basic principles of the two types of processes are well known, a greater effort is needed towards the development of more efficient and stable catalysts under the severe operation conditions imposed by the reaction itself, as well as the need for suitable reaction design to minimize the extent of the homogeneous reaction. The alternative process is to obtain synthesis gas (CO/H2) in a first step through steam reforming followed by a second Fischer-Tropsch hydrogenation step. However, the unfavorable energetic balance of the reforming step and the absence of selective catalysts in the latter to obtain a narrow molecular weight distribution currently leads to compromise in solutions. Among these, the high molecular weight alcohol synthesis and the recently developed Shell middle distillate synthesis (SMDS) appear to be very attractive. Of no less importance are the reactions which incorporate a CO molecule into alcohols or olefins via carbonylations and hydroformylations. Within this framework, the use of organometallic complexes anchored to functionalized polymeric matrices initiated a very intense research activity, particularly in the development of stable catalysts.

Mayagoitia, Vicente

2004 Catalysis Letters

doi: 10.1007/BF00811771

Fundamental principles involved in the characterization of porous networks are presented through the development of three essential steps: (i) proposition of a convenient model of the porous network, (ii) recognition of the mechanisms governing the processes related to the experiments of textural determination, and (iii) interpretation of the experimental data, taking into account the two preceding steps.

Ribeiro, F.

2004 Catalysis Letters

doi: 10.1007/BF00811772

The selectivity of zeolite catalysts can be adjusted by modifying the characteristics of the active sites, and by modifying the diffusion path of the reactants and products, as well as the space available around the active sites. In this context shape selectivity, in its multiple aspects, and the most important parameters that influence it, will be discussed. Some examples of selectivity improvement by modification of the zeolite porosity in particular grafting or deposition of various compounds on the outer surface of the crystallite are given.

Castro, A.

2004 Catalysis Letters

doi: 10.1007/BF00811773

Selective dehydrogenation of high molecular weight linear paraffins is an important process step for the production of biodegradable detergents. Pt, PtSn, PtGe and PtPb supported on γ-A12O3 doped with alkaline metals were characterized and tested in then-decane dehydrogenation reaction. When alkaline metals are added to Pt/Al2O3 a promoting effect on the selectivity to olefins in then-decane dehydrogenation is observed. Regarding PtSn/Al2O3 -doped catalysts their performance depends on the alkaline metal used as dopant, the Sn content and the preparation method. Moreover these bimetallic catalysts show a better olefin yield and a lower selectivity to gases and aromatics than the monometallic platinum catalysts. PtGe and PtPb based catalysts have an analogous behavior to the PtSn one but its selectivity to olefins is lower.

Andreu, Paulino

2004 Catalysis Letters

doi: 10.1007/BF00811774

The present paper describes the development of a catalyst for the fluid catalytic cracking process of gasoils. The catalyst produced is to maximize the high octane components in the gasolines and the liquefied gases for petrochemical use. The results obtained in the riser type pilot plants of the Compañia Española de Petróleo, S.A. (CEPSA), and INTEVEP, S.A., R&D Center of Petróleos de Venezuela, S.A. are also reported. Finally, information is given on the technical-economic feasibility of a prototype plant for manufacturing this type of catalyst with an annual capacity often thousand tons.