Progress in the Development of Electrodeposited Catalysts for Direct Liquid Fuel Cell Applications

Fuel cells are a key enabling technology for the future economy, thereby providing power to portable, stationary, and transportation applications, which can be considered an important contributor towards reducing the high dependencies on fossil fuels. Electrocatalyst plays a vital role in improving the performance of the low temperature fuel cells. Noble metals (Pt, Pd) supported on carbon have shown promising performance owing to their high catalytic activity for both electroreduction and electrooxidation and have good stability. Catalyst preparation by electrodeposition is considered to be simple in terms of operation and scalability with relatively low cost to obtain high purity metal deposits. This review emphasises the role of electrodeposition as a cost-effective method for synthesising fuel cell catalysts, summarising the progress in the electrodeposited Pt and Pd catalysts for direct liquid fuel cells (DLFCs). Moreover, this review also discusses the technological advances made utilising these catalysts in the past three decades, and the factors that impede the technological advancement of the electrodeposition process are presented. The challenges and the fundamental research strategies needed to achieve the commercial potential of electrodeposition as an economical, efficient methodology for synthesising fuel cells catalysts are outlined with the necessary raw materials considering current and future savings scenario.

AN IMPROVED METHOD FOR THE PREPARATION OF PHLOROGLUCINOL FROM 1,3,5-TRINITROBENZENE

Статья посвящена способу получения флороглюцина, представляющего интерес в качестве основы для конструирования лекарственных средств, полимеров различного назначения и малочувствительного взрывчатого вещества 1,3,5-триамино-2,4,6-тринитробензола. Современным и наиболее экологичным методом получения флороглюцина является каталитическое гидрирование 1,3,5-тринитробензола на палладиевом катализаторе до 1,3,5-триаминобензола и его последующий гидролиз. Использование палладиевых катализаторов позволяет проводить восстановление в мягких условиях, но их высокая стоимость обуславливает потребность в поиске путей снижения расхода палладия и, соответственно, себестоимости процесса. В данном исследовании показано, что использование 1 %-го Pd/сибунит (50 % к массе субстрата) в сочетании с водно-ацетоновым раствором в качестве среды при проведении гидрирования способствует более длительному сохранению активности катализатора. Установлено, что оптимальное соотношение ацетона и воды находится в диапазоне от 4:1 до 7:1. В этом случае может быть проведено до 20 циклов гидрирования без добавления свежего катализатора, за счет чего удается снизить расход палладия в три раза по сравнению с другими известными методиками. Кроме того, подход позволяет исключить из схемы синтеза токсичный растворитель метанол. Триаминобензол, полученный в ходе гидрирования, без выделения подвергается гидролизу в присутствии серной кислоты с образованием флороглюцина. Изучена зависимость выхода флороглюцина от мольного соотношения серной кислоты и тринитробензола. Установлено, что оптимальное соотношение серная кислота : тринитробензол составляет 2,0-2,4 моль/моль. Суммарный выход флороглюцина составляет 76 % в пересчете на тринитробензол. The study is concerned with a synthetic method for phloroglucinol that is of great concern as a scaffold for designing medicinal drugs, different-purpose polymers and the insensitive explosive 1,3,5-triamino-2,4,6-trinitrobenzene. The current and most eco-benign method for the synthesis of phloroglucinol is through catalytic hydrogenation of 1,3,5-trinitrobenzene over the Pd catalyst to 1,3,5-triaminobenzene followed by its hydrolysis. The use of Pd catalysts allows the reduction under mild conditions, but their high cost necessitates the need to find ways how to spare the Pd usage and, consequently, the process cost. Here we demonstrated that the use of 1% Pd/Sibunite (50% to substrate weight) combined with a water-acetone solution as the medium in hydrogenation allows the catalyst to keep active longer. The optimum acetone-to-water ratio was found to be between 4:1 and 7:1. In this case, as many as 20 hydrogenation runs can be done without a fresh catalyst added whereby the Pd usage can be lowered threefold when compared to the other common methods in use. Besides, this approach allows the toxic solvent methanol to be expelled from the synthetic protocol. Triaminobenzene resulting from the hydrogenation without isolation undergoes hydrolysis in the presence of sulfuric acid to furnish phloroglucinol. The relationship between the phloroglucinol yield and the molar ratio of sulfuric acid and trinitrobenzene was also explored. The optimum sulfuric acid-to-trinitrobenzene ratio was found to be 2.0-2.4 mol/mol. The overall yield of phloroglucinol was 76% on a trinitrobenzene basis.

Renewable Hydrocarbon Production via Rapeseed Oil Hydrotreatment Over Palladium Catalysts

The effect of SiO2-Al2O3 (Pd5%/SA), activated carbon (Pd5%/C) and Al2O3 (Pd5%/A) supported palladium (5%) catalysts on renewable hydrocarbon synthesis via rapeseed oil hydrotreatment was investigated. The hydrotreatment experiments were carried out in solvent free medium under initial H2 pressure 100 bar and at 340 °C temperature for 120 min using catalyst amount 5%. Gas chromatography-mass spectrometry (GC/MS) analysis were used for estimation of hydrocarbon content in the obtained samples. Pd5%/SA catalyst provided complete conversion of rapeseed oil into marketable liquid renewable hydrocarbons without presence of oxygen containing substances under studied hydrotreatment conditions. Moreover, all tested Pd catalysts gave narrow range of linear saturated hydrocarbons (n-C15-C19). Pd5%/C and Pd5%/A catalysts gave partial feedstock conversion into hydrocarbons even in long residence time. Overall liquid hydrocarbon yields were from 55.3% to 82.3%.

Investigating (Pseudo)-Heterogeneous Pd-Catalysts for Kraft Lignin Depolymerization under Mild Aqueous Basic Conditions

Lignin is one of the main components of lignocellulosic biomass and corresponds to the first renewable source of aromatic compounds. It is obtained as a by-product in 100 million tons per year, mainly from the paper industry, from which only 2–3% is upgraded for chemistry purposes, with the rest being used as an energy source. The richness of the functional groups in lignin makes it an attractive precursor for a wide variety of aromatic compounds. With this aim, we investigated the Pd-catalyzed depolymerization of lignin under mild oxidizing conditions (air, 150 °C, and aqueous NaOH) producing oxygenated aromatic compounds, such as vanillin, vanillic acid, and acetovanillone. Palladium catalysts were implemented following different strategies, involving nanoparticles stabilized in water, and nanoparticles were supported on TiO2. Significant conversion of lignin was observed in all cases; however, depending on the catalyst nature and the synthetic methods, differences were observed in terms of selectivity in aromatic monomers, mainly vanillin. All these aspects are discussed in detail in this report, which also provides new insights into the role that Pd-catalysts can play for the lignin depolymerization mechanism.

H2 Production from Formic Acid Using Highly Stable Carbon-Supported Pd-Based Catalysts Derived from Soft-Biomass Residues: Effect of Heat Treatment and Functionalization of the Carbon Support

The production of hydrogen from liquid organic hydrogen carrier molecules stands up as a promising option over the conventional hydrogen storage methods. In this study, we explore the potential of formic acid as a convenient hydrogen carrier. For that, soft-biomass-derived carbon-supported Pd catalysts were synthesized by a H3PO4-assisted hydrothermal carbonization method. To assess the impact of the properties of the support in the catalytic performance towards the dehydrogenation of formic acid, three different strategies were employed: (i) incorporation of nitrogen functional groups; (ii) modification of the surface chemistry by performing a thermal treatment at high temperatures (i.e., 900 °C); and (iii) combination on both thermal treatment and nitrogen functionalization. It was observed that the modification of the carbon support with these strategies resulted in catalysts with enhanced performance and outstanding stability even after six consecutive reaction cycles, thus highlighting the important effect of tailoring the properties of the support.