The development of visible-light active titanium dioxide is one of the key challenges in photocatalysis that stimulates the development of TiO2-based composite materials and methods for their synthesis. Here, we report the use of pristine and Pt-modified dark titanium dioxide prepared via pulsed laser ablation in liquid (Nd:YAG laser, 1064 nm, 7 ns) for photocatalytic hydrogen evolution from alcohol aqueous solutions. The structure, textural, optical, photoelectrochemical, and electrochemical properties of the materials are studied by a complex of methods including X-ray diffraction, low-temperature nitrogen adsorption, electrophoretic light scattering, diffuse reflection spectroscopy, photoelectrochemical testing, and electrochemical impedance spectroscopy. Both the thermal treatment effect and the effect of modification with platinum on photocatalytic properties of dark titania materials are studied. Optimal compositions and experimental conditions are selected, and high photocatalytic efficiency of the samples in the hydrogen evolution reaction (apparent quantum yield of H2 up to 0.38) is demonstrated when irradiated with soft UV and blue LED, i.e., 375 and 410 nm. The positive effect of low platinum concentrations on the increase in the catalytic activity of dark titania is explained.
Benzene hydrogenation in steady‐state and unsteady‐state regimes over sulfide Ni‐W/γ‐Al2O3 catalyst is studied. The mechanism and dynamic model of hydrogenation and hydrogenolysis active sites transformation are proposed. The reactions were shown to be quasi steady‐state ones with slow poisoning of both hydrogenation and hydrogenolysis active sites by the formation of intermediate surface compounds of sulfur. The dynamic behavior was described by the proposed model with sufficient accuracy.
This study focuses on problems related to fouling of heat exchange equipment of diesel hydrotreatment (DHT) processes and diagnostics of heat exchanger condition. Fouling is a critical aspect directly affecting the performance of a heat exchanger. The objective of this study is to determine, using a mathematical model, an optimal timing for cleaning of DHT heat exchange equipment for the removal of fouling. In accordance with results of calculations performed with a mathematical model of a typical DHT unit (L-24/9), condition assessment index for a heat exchanger of the reactor section increases from 1 to 1.37 when shell side fouling factor increases from 0.00003 to 0.00150 (°C·h·m2)/kJ. This results in a decrease of the feed temperature at the vessel outlet, and an increase of costs related to additional fuel consumed by heaters by over RUB 1 million/month. Therefore, activities related to the cleaning of tube bundles of reactor section heat exchangers pay back in full in 1 month, as fuel savings brought about by the cleaning exceeded 12.6%. In order to carry out diagnostics of heat exchange surface fouling and to determine an optimal timing for tube bundle cleaning in order to remove deposits, vessels have to be equipped with transmitters measuring temperatures of all inlet/outlet streams. The use of on-line heat exchanger diagnostics makes it possible to choose an optimal timing of tube bundle cleaning based on comparability of costs related to additional fuel consumption and cleaning costs.
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