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SO2 adsorption and desorption on NaX and NaY zeolites, as a function of contact time and temperature, were studied combining in situ FTIR (diffuse reflectance with controlled chamber) and thermogra...

Conductive carbon-ceramic composites have been prepared from coal tar pitch and a ceramic already molded as a monolith having a honeycomb structure. The material has been obtained by subjecting both components to a heat treatment in N2 to a maximum temperature of either 1073 K or 1273 K. The starting ceramic and the composites have been characterized by scanning electron microscopy, EDX, thermogravimetry and X-ray diffraction. Conductivity measurements and electrochemical behavior have been also carried out. The results obtained reveal that the highest conductivities are obtained in those samples heated to the maximum temperature studied. Stability towards oxygen increases with treatment temperature, reaching the samples treated to 1273 K for 2 hours, a gasification temperature similar to the graphite material studied. Additionally, the composites exhibit a high electrochemical stability that makes these materials very promising to be used as electrodes and/or as electrocatalysts support. OCICARBON (Project No. C23-353); DGICYT (Project No. PB93-09345).

SAXS measurements have been made for two series of ACF prepared by CO 2 and steam activation.

The present work extends previous investigations, related to the calcium-catalyzed carbon gasification, by using a technique called temperature-programmed reaction (TPR) under CO 2 . The purpose is to confirm and to complete the carbon gasification mechanism catalyzed by calcium deduced from earlier TPD studies. The TPR technique has the advantage of studying the catalyst behavior under conditions closer to the gasification reaction than in the case of TPD experiments

A formal specification of the purchase phase in the SET protocol (Secure Electronic Transaction), an e-commerce protocol by Visa and MasterCard, is presented. It is modelled by means of a True Concurrency Timed Process Algebra called BTC which takes into account that the (limited amount of) available resources in a system have to be shared by all the processes. We have considered heterogeneous resources and we extend the algebra with the intention of representing the actions which use the shared resources and how many resources of each type the system has at its disposal.

This paper describes the different procedures applied for the preparation of general purpose carbon fibers from four coal tar pitches. The four raw materials have a low softening point (of about 373 K) for this application and, hence, must be subjected to a treatment before spinning to increase this temperature. The treatments applied are the following: (i) heating in N2, (ii) heating in air, (iii) consecutive heating in N2 and air, and (iv) blending of the coal tar pitch with a petroleum one and further treatment in air. The changes in chemical composition, softening point and yield of the treatments used have been followed by different techniques. Only treatments (iii) and (iv) produce materials with an adequate viscosity for spinning and a sufficiently high softening point to be transformed in carbon fibers. The carbon fibers obtained have similar mechanical properties to those prepared in a previous work from a suitable petroleum pitch with the same experimental system. However, the mechanical properties of these fibers are inferior to those of a commercial carbon fiber, the differences being due to the lower diameter of the commercial fibers.

The state of the metallic phase of PtSn/C catalysts prepared by coimpregnation and successive impregnation on purified and H 2 O 2 -functionalized carbons as supports was studied by TPD, TPR, H 2 chemisorption, XPS, and test reactions. Furthermore, the characteristics of the metallic structures were related with the catalytic behaviors in the selective hydrogenation reaction of carvone in liquid phase. In PtSn/C samples, most of the Sn would be in intimate contact with Pt, and the surface of the reduced bimetallic catalysts would be composed of metallic platinum, Sn(II), and/or Sn(IV) species, and small amounts of zerovalent tin, probably forming alloys with Pt 0 . The high selectivity of these bimetallic PtSn/C catalysts for the production of unsaturated alcohols in the reaction of carvone hydrogenation would be due to the action not only of the promoter (Sn) but also of the support (carbon).

The experiment described in this paper is concerned with the use of activated carbon as a catalyst for oxidation of SO2 to sulfuric acid. The experiment is a good example of heterogeneous catalysis and environmental clean-up. It is simple to set up and uses a conductometer (conductivity meter) to follow the reaction. We describe the experiment in detail, from the preparation of sulfur dioxide to its oxidation by oxygen, the reaction catalyzed by activated carbon. Typical results and suggestions for performing a larger study of the kinetics of the reaction are presented.

Molecular sieve properties of general-purpose carbon fibres (GPCFs) from different origins are studied. Selectivity of the materials for CO2 and CH4 separation and uptake of these gases are analysed and compared with a commercial pelleted carbon molecular sieve appropriate for this process. A set of four GPCFs, one of them commercially available, obtained from petroleum or coal tar pitches is used in this work. Kinetics of CO2 and CH4 uptake at different pressures and temperatures have been followed. The results obtained show that the GPCFs have a high selectivity to CO2, the kinetics of the process being very slow. The treatments, which comprise either the elimination of surface oxygen groups or controlled gasification, produce materials with a high selectivity and CO2 uptake and fast kinetics. In this sense, the general-purpose carbon fibres can have a performance as good as a commercial carbon molecular sieve.

Photocatalysis represents a promising technology that might alleviate the current environmental crisis. One of the most representative photocatalysts is graphitic carbon nitride (g-C3N4) due to its stability, cost-effectiveness, facile synthesis procedure, and absorption properties in visible light. Nevertheless, pristine g-C3N4 still exhibits low photoactivity due to the rapid recombination of photo-induced electron-hole (e−-h+) pairs. To solve this drawback, Z-scheme photocatalysts based on g-C3N4 are superior alternatives since these systems present the same band configuration but follow a different charge carrier recombination mechanism. To contextualize the topic, the main drawbacks of using g-C3N4 as a photocatalyst in environmental applications are mentioned in this review. Then, the basic concepts of the Z-scheme and the synthesis and characterization of the Z-scheme based on g-C3N4 are addressed to obtain novel systems with suitable photocatalytic activity in environmental applications (pollutant abatement, H2 production, and CO2 reduction). Focusing on the applications of the Z-scheme based on g-C3N4, the most representative examples of these systems are referred to, analyzed, and commented on in the main text. To conclude this review, an outlook of the future challenges and prospects of g-C3N4-based Z-scheme photocatalysts is addressed. This research was funded by European Union-Next Generation EU, MINECO, and University of Alicante: MARSALAS21-09, Generalitat Valenciana: CDEIGENT/2018/027, University of Alicante: GRE20-19-A. PID2021-123079OB-I00 project funded by MCIN/AEI/10.13039/501100011033 and “ERDF A way of making Europe”, European Union’s Horizon 2020 research and innovation programme: Grant Agreement 101002219 and Generalitat Valenciana: Proyecto Prometeo CIPROM/2021/70.