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Papers by antonio chica

Catalysis Today, 2003

Applying accelerated techniques for catalyst synthesis and testing and a stochastic experimental ... more Applying accelerated techniques for catalyst synthesis and testing and a stochastic experimental design, two catalytic systems based on SO 4 2− /ZrO 2 and WO x /ZrO 2 were seen as active and selective for n-paraffin isomerization. After three optimization cycles, a new catalyst formulation based on promoted SO 4 2− /ZrO 2 with improved activity and selectivity has been found. Characterization of the best catalysts generated in each cycle has been done. Activity and selectivity of the best catalyst found has been tested in the isomerization of a simulated industrial feed composed by n-pentane, n-hexane and n-heptane. For the second best catalytic system, i.e. WO x /ZrO 2 , the influence of tungsten content, promotor (Ce), nature of the starting precursor salt (sulfate, nitrate or chloride), and catalyst calcination temperature was studied using a factorial design. The relevance of the interaction between salt precursor and calcination temperature is discussed.

Journal of Catalysis, 2000

Molecular dynamics techniques have been used to simulate the diffusion of n-heptane, 2-methyl-hex... more Molecular dynamics techniques have been used to simulate the diffusion of n-heptane, 2-methyl-hexane, 2,3-dimethylpentane, 1-propyl-2-methyl-cyclopropane, and 1-isopropyl-2methyl-cyclopropane in two unidimensional medium pore zeolites, ZSM-48 and Theta-1. In this way the isomerisation reactions nheptane → 2-methyl-hexane → 2,3-dimethyl-pentane were studied, also including the cyclopropane reaction intermediates. The self-diffusivity of these sorbates and its variation with the channel size of the zeolite is studied. The diffusion in the slightly larger channels of ZSM-48 is faster than that found in Theta-1, and an effect of product shape selectivity, especially in Theta-1, is observed in the reaction going from the monomethyl to the dimethyl isomer. An excess of the monobranched/dibranched ratio is then expected in Theta-1 with respect to ZSM-48. The role of the external versus internal surface in the reaction products has been investigated by carrying out catalytic isomerisation of n-hexadecane in Theta-1 by depleting the external surface of acid sites. The results show that terminal monobranched alkanes can be formed inside the pores, and that dibranched alkanes are mainly formed at the external surface by isomerisation of the monobranched products.

Journal of Catalysis, 2000

The pore topology of a recently synthesized zeolite IM-5 has been determined by means of catalyti... more The pore topology of a recently synthesized zeolite IM-5 has been determined by means of catalytic test reactions, i.e., n-decane hydroisomerization-cracking, m-xylene isomerization-disproportionation, n-hexadecane isodewaxing, and adsorption-microcalorimetry of molecules with different sizes and shapes (n-hexane, toluene, m-xylene, and 1,3,5 trimethylbenzene). It has been found that the channel network consists of a system of unidirectional 10 MR with lobes or side pockets, or crossing 10 membered ring pores with a pore diameter somewhat smaller than those in ZSM-5. This structure offers interesting shape selectivity features for catalytic reactions.

Catalysis Today, 2001

The hydroisomerization-hydrocracking of nC 5 -nC 7 is studied with a 12MR unidirectional zeolite ... more The hydroisomerization-hydrocracking of nC 5 -nC 7 is studied with a 12MR unidirectional zeolite (ITQ-4). Selectivity and kinetic parameters indicate that differences in pore topology are more important than acidity for determining isomerization selectivity. The adsorption of the paraffins is determined by van der Waals interactions.

Journal of Catalysis, 1999

The hydroisomerization of n-heptane to dibranched and tribranched products for producing high oct... more The hydroisomerization of n-heptane to dibranched and tribranched products for producing high octane gasoline has been studied using unidirectional 12 Membered Ring (MR) zeolites with different pore diameters, and zeolites with other pore topologies including one with connected 12 × 10 MR pores and two tridirectional 12 MR zeolites. Besides the pore topology, the crystallite size of the zeolite was seen to be of paramount importance for improving activity and selectivity. In a second part of the work, a Light Straight Run naphtha including n-pentane and n-hexane and another feed containing n-pentane, n-hexane, and n-heptane have been successfully isomerized using a nanocrystalline Beta (BEA) zeolite. This can be a favourable alternative to the commercial zeolite catalyst based on mordenite (MOR), especially when n-heptane is present in the feed.

Combinatorial catalysis [1–6] is a methodology where a large number of new materials are prepared... more Combinatorial catalysis [1–6] is a methodology where a large number of new materials are prepared and tested in a parallel fashion. The global search/optimisation strategy is the main difference with the traditional catalyst research and should allow the reduction of the number of experiments needed to find an optimal catalyst composition. Combinatorial catalysis involves the coordination of: high-throughput systems [7–12] for preparation, characterisation and catalytic test; large information data management; and rapid optimisation techniques. This promising approach requires therefore the development and optimisation of the following items: (i) high-throughput equipment, which allows the reliable preparation and characterisation/testing preferentially under realistic conditions of larger quantities of materials (ii) optimisation techniques, adapting their structure and parameters by implementing the chemical knowledge/experience of the experts. With this, it would be possible to increase the number of variables to study and this would result in a potentially rather more powerful final catalyst and shorter search times. Indeed, if this methodology is properly followed it can be very helpful in the scientific understanding of catalysis.

Journal of Physical Chemistry B, 2000

ABSTRACT

Journal of Catalysis, 2006

The silicoaluminophosphates SAPO-11 isodewaxing catalysts were synthesized with varying Si conten... more The silicoaluminophosphates SAPO-11 isodewaxing catalysts were synthesized with varying Si content following conventional methods and using a route involving the presence of surfactant. Smaller crystal size (∼80 nm) and higher external surface areas were found for the samples prepared with surfactant. This synthesis route using surfactant gives SAPO-11 samples with greater numbers of stronger acid sites than those prepared by conventional synthesis. The 29 Si MAS-NMR spectra obtained for samples containing the same amount of silicon showed that SAPO-11 prepared with surfactant contains a higher relative concentration of Si (nAl, 4-nSi), 0 < n < 4, border environments, whereas large patches of Si(4Si) are predominant in the samples prepared without surfactant. These results support the idea that introducing surfactant during synthesis contributes to better Si dispersion, decreasing the size of Si(4Si) patches and increasing the number and strength of acid sites. The hydroconversion of n-hexadecane on Pt/SAPO-11 samples indicates that the samples synthesized with surfactant with similar Si content and very close crystallite size to those synthesized by conventional methods are much more active and selective for the hydroisomerization of long-chain n-paraffins.

Chemie Ingenieur Technik, 2007

The hydroisomerization of n-octane has been catalyzed by different zeolitic structures with large... more The hydroisomerization of n-octane has been catalyzed by different zeolitic structures with large pore size (12 MR). It has been seen that channel topology, chemical composition, crystal size, and adsorption properties are of paramount importance for improving the isomerization activity and selectivity. Nanocrystalline beta zeolite (30 nm) with large pore size (0.66 × 0.67 and 0.56 × 0.56 nm), and high aluminum content (Si/Al = 16), was the best catalyst to produce multibranched isomers. Cracking reactions also occur together with isomerization and the product distribution will depend on the rate constant and relative activation energies of isomerization, desorption, and cracking. Furthermore, a complete kinetic study of n-octane isomerization has been carried out with beta zeolite, and kinetic rate constants, heats of adsorption, and activation energies have been determined for each individual isomerization step. The rate of isomerization of n-octane to monobranched products was found to be faster than the rate of cracking of dibranched products and the rate of isomerization of mono- to dibranched products. It should be possible to obtain high yields of dibranched alkanes by distillation and recycling units, or by using membrane reactors.

Catalysis Today, 2003

This work is focused on the practical application of artificial intelligent techniques in chemica... more This work is focused on the practical application of artificial intelligent techniques in chemical engineering. Specifically, it describes an application of artificial neural networks for modelling the kinetics of a chemical reaction using methods not based in a kinetic model. Thus, neural networks have been used to model the behaviour of one catalyst under different reaction conditions for a specific reaction, i.e. n-octane isomerisation. Secondly, trained neural networks were used to model successfully another reaction with a similar reaction network.

Journal of Catalysis, 2006

The oxidative desulfurization (ODS) of model sulfur-containing compounds (thiophene, 2-methylthio... more The oxidative desulfurization (ODS) of model sulfur-containing compounds (thiophene, 2-methylthiophene, benzothiophene, 2-methylbezothiophene, dibenzothiophene, 4-methyldibenzothiophene, and 4,6-dimethyldibenzothiophene) with tert-butyl hydroperoxide on different metalcontaining molecular sieves has allowed the study the role of the electronics and geometry of the reactant as well as the pore dimensions, topology, and adsorption properties of the catalyst on the rate of desulfurization. The best catalysts were then studied for the ODS of simulated and industrial diesel in a continuous fixed-bed reactor. MoO x /Al 2 O 3 catalysts were active, but rapid deactivation occurs due to metal leaching and sulfone adsorption. Calcined Ti-MCM-41 was more active, did not leach Ti, and deactivated more slowly than MoO x /Al 2 O 3 . The amount of adsorbed sulfone was strongly reduced by decreasing the polarity of the Ti-MCM-41 by silylation, with the corresponding increase in catalyst activity and lifetime.

Applied Catalysis A-general, 2003

By means of combinatorial techniques (high-throughput catalyst preparation and testing systems, a... more By means of combinatorial techniques (high-throughput catalyst preparation and testing systems, and a genetic algorithm (GA)), a search of new more tioresistant catalysts for low temperature isomerization of light paraffins has been conducted. After three evolving cycles catalysts have been found that not only are active and selective but also are more resistant to deactivation by water and sulphur than