Photo-Thermal Dry Reforming of Methane with PGM-Free and PGM-Based Catalysts: A Review.

Dry reforming of methane (DRM) is considered one of the most promising technologies for efficient greenhouse gas management thanks to the fact that through this reaction, it is possible to reduce CO2 and CH4 to obtain syngas, a mixture of H2 and CO, with a suitable ratio for the Fischer-Tropsch production of long-chain hydrocarbons. Two other main processes can yield H2 from CH4, i.e., Steam Reforming of Methane (SRM) and Partial Oxidation of Methane (POM), even though, not having CO2 as a reagent, they are considered less green. Recently, scientists' challenge is to overcome the many drawbacks of DRM reactions, i.e., the use of precious metal-based catalysts, the high temperatures of the process, metal particle sintering and carbon deposition on the catalysts' surfaces. To overcome these issues, one proposed solution is to implement photo-thermal dry reforming of methane in which irradiation with light is used in combination with heating to improve the efficiency of the process. In this paper, we review the work of several groups aiming to investigate the pivotal promoting role of light radiation in DRM. Focus is also placed on the catalysts' design and the progress needed for bringing DRM to an industrial scale.

Porous Organic Polymers for Selective Palladium Recovery and Heterogeneous Catalysis.

Palladium (Pd) recycling from waste materials is an important approach in order to meet the growing demand for Pd originating from its broad range of applications including automotive industry, electronics and catalysis. In this article, we discuss the design principles of solid-sorbents for efficient recovery of Pd from waste sources with a particular emphasis on porous organic polymers (POPs), which emerged as promising porous materials for Pd recovery due to their tunable chemical functionality, stability and porosity. We discuss the critical role of binding sites and porosity in the Pd uptake capacity, adsorption kinetics and selectivity. We also highlight the use of captured Pd within the polymer networks as heterogeneous catalysts for cross-coupling reactions.

Life Cycle Assessment and Environmental Life Cycle costing of a unitised regenerative fuel cell stack.

Life Cycle Assessment (LCA) and Environmental Life Cycle Costing (eLCC) are useful methods for evaluating the environmental, energy and economic performances of innovative energy storage technologies. By using these methods, the production process of a small Polymer Electrolyte Membrane Unitized Regenerative Fuel Cell (PEM-URFC) stack has been investigated, aiming to assess its environmental, energy and economic impacts at the early design stage and to identify the contributions of its various components on these impacts. Indeed, the PEM-URFC stack includes Critical Raw Materials that affect the product's sustainability. Results show that the highest contributions are associated with the platinum group metals used for the catalyst and, to a lesser degree, the materials and energy used for the bipolar plates and porous transport layers. However, considering that the datasets for representing the impacts of one of the electrocatalysts (Iridium Ruthenium Oxide) are still missing in LCA commercial databases and literature, a sensitivity analysis is performed assuming its impact to be similar to that of other Platinum Group Metals (PGMs) extracted with them (e.g., Platinum, Nickel, Palladium, etc.). The analysis shows a high difference in results due to data and methodological assumptions, making the assimilation of Iridium Ruthenium Oxide to Rhodium the worst scenario, increasing environmental impacts by 37.54 %, energy impacts by 40.48 % and environmental price by 45.08 %. Moreover, the study identified issues for applying life cycle thinking approaches on URFC devices that must be resolved in future studies (e.g., increase the reliability of catalyst inventory data or improve guidelines on energy storage technologies).

Precipitation of Pt, Pd, Rh, and Ru Nanoparticles with Non-Precious Metals from Model and Real Multicomponent Solutions.

This article presents studies on the precipitation of Pt, Pd, Rh, and Ru nanoparticles (NPs) from model and real multicomponent solutions using sodium borohydride, ascorbic acid, sodium formate, and formic acid as reducing agents and polyvinylpyrrolidone as a stabilizing agent. As was expected, apart from PGMs, non-precious metals were coprecipitated. The influence of the addition of non-precious metal ions into the feed solution on the precipitation yield and catalytic properties of the obtained precipitates was studied. A strong reducing agent, NaBH4 precipitates Pt, Pd, Rh, Fe and Cu NPs in most cases with an efficiency greater than 80% from three- and four-component model solutions. The morphology of the PGMs nanoparticles was analyzed via SEM-EDS and TEM. The size of a single nanoparticle of each precipitated metal was not larger than 5 nm. The catalytic properties of the obtained nanomaterials were confirmed via the reaction of the reduction of 4-nitrophenol (NPh) to 4-aminophenol (NAf). Nanocatalysts containing Pt/Pd/Fe NPs obtained from a real solution (produced as a result of the leaching of spent automotive catalysts) showed high catalytic activity (86% NPh conversion after 30 min of reaction at pH 11 with 3 mg of the nanocatalyst).

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Platinum group metals (PGMs) present a variety of forms in the environment, and analysis of speciation is essential for identifying their ecological risk. Here, we reviewed the methods for the morphological analysis of three major PGMs (platinum, palladium and rhodium) in the environment, including chemical sequential extraction, hyphenated techniques for instruments, computer simulations. We outlined the types, characteristics and applications of these methods, elaborated the weaknesses, and provided prospects for future development. Among them, chemical sequential extraction is universally applied in the morphological analysis of solid-phase samples, with diverse extraction conditions and procedures proposed in the current study. However, it has not been well standardized. The hyphenated techniques for instruments have significant advantages for the determination of elemental forms in solution, of which capillary electrophoresis system can separate similar substances with the same electrophoresis ability. Liquid chromatography systems have better performance in terms of separation capacity and detection limit. The computer simulations further expand the access to morphological analysis, enabling complex morphological calculations. It was proposed to combine multiple methods in the future to continuously improve the accuracy of analytical techniques by complementing and optimizing each other.

In vitro permeation of platinum through African and Caucasian skin.

The majority of the South African workforce are Africans, therefore potential racial differences should be considered in risk and exposure assessments in the workplace. Literature suggests African skin to be a superior barrier against permeation and irritants. Previous in vitro studies on metals only included skin from Caucasian donors, whereas this study compared the permeation of platinum through African and Caucasian skin. A donor solution of 0.3 mg/ml of potassium tetrachloroplatinate (K2PtCl4) dissolved in synthetic sweat was applied to the vertical Franz diffusion cells with full thickness abdominal skin. Skin from three female African and three female Caucasian donors were included (n=21). The receptor solution was removed at various intervals during the 24 h experiment, and analysed with high resolution inductively coupled plasma-mass spectrometry (ICP-MS). Skin was digested and analysed by inductively coupled plasma-optical emission spectrometry (ICP-OES). Significantly higher permeation of platinum through intact African skin (p=0.044), as well as a significantly higher mass of platinum retention in African skin in comparison with Caucasian skin (p=0.002) occurred. Significant inter-donor variation was found in both racial groups (p<0.02). Results indicate that African workers have increased risk of dermal permeation and therefore possible sensitisation caused by dermal exposure to platinum salts. These results are contradictory to limited literature suggesting a superior barrier in African skin and further investigation is necessary to explain the higher permeation through African skin.

In vitro permeation of platinum and rhodium through Caucasian skin.

During platinum group metals (PGMs) refining the possibility exists for dermal exposure to PGM salts. The dermal route has been questioned as an alternative route of exposure that could contribute to employee sensitisation, even though literature has been focused on respiratory exposure. This study aimed to investigate the in vitro permeation of platinum and rhodium through intact Caucasian skin. A donor solution of 0.3mg/ml of metal, K2PtCl4 and RhCl3 respectively, was applied to the vertical Franz diffusion cells with full thickness abdominal skin. The receptor solution was removed at various intervals during the 24h experiment, and analysed with high resolution ICP-MS. Skin was digested and analysed by ICP-OES. Results indicated cumulative permeation with prolonged exposure, with a significantly higher mass of platinum permeating after 24h when compared to rhodium. The mass of platinum retained inside the skin and the flux of platinum across the skin was significantly higher than that of rhodium. Permeated and skin retained platinum and rhodium may therefore contribute to sensitisation and indicates a health risk associated with dermal exposure in the workplace.