TiO2-supported Pt species have been widely applied in numerous critical reactions involving photo-, thermo-, and electrochemical-catalysis for decades. Manipulation of the state of the Pt species in Pt/TiO2 catalysts is crucial for fine-tuning their catalytic performance. Here, we report an interesting discovery showing the epitaxial growth of PtO2 atomic layers on rutile TiO2, potentially allowing control of the states of active Pt species in Pt/TiO2 catalysts. The presence of PtO2 atomic layers could modulate the geometric configuration and electronic state of the Pt species under reduction conditions, resulting in a spread of the particle shape and obtaining a Pt/PtO2/TiO2 structure with more positive valence of Pt species. As a result, such a catalyst exhibits exceptional electrocatalytic activity and stability toward hydrogen evolution reaction, while also promoting the thermocatalytic CO oxidation, surpassing the performance of the Pt/TiO2 catalyst with no epitaxial structure. This novel epitaxial growth of the PtO2 structure on rutile TiO2 in Pt/TiO2 catalysts shows its potential in the rational design of highly active and economical catalysts toward diverse catalytic reactions. 

Significance of Epitaxial Growth of PtO2 on Rutile TiO2 for Pt/TiO2 Catalysts.

For the adsorptive separation of propylene/propane (C3H6/C3H8) with high similarities in physiochemical properties, size-exclusive effect is highly attractive that can realize the superior selectivity. Nevertheless, the required narrow pores would unavoidably resist mass transfer of C3H6 molecules. To minimize the hindered diffusion, we report a systematic pore-engineering study in a family of carbon microspheres with fine-tuning pore sizes by exceptional activation-free method. The manipulation of pores was realized by varied temperature during glucose hydrothermal synthesis with acid additive as catalysis. Among as-obtained carbon analogs, GC-190 with optimal pore size closing to the kinetic diameter of C3H8 (5.11 Å), exhibited outstanding C3H6/C3H8 size-sieving property as well as fast C3H6 kinetics plausibly. However, GC-230 with smaller pores closing to the size of C3H6 (4.68 Å) showed sluggish C3H6 diffusion despite retaining size-sieving effect. The C3H6 diffusion constant rate (D') of 1.21 × 10−2 min−1 on GC-190 is about two orders of magnitude higher than GC-230 of 2.29 × 10−4 min−1. DFT simulation further supports the remarkably reduced diffusion energy barrier of C3H6 by sub-angstrom level increased pore size. This study may deepen the understanding of gas diffusion in confined narrow pores and provides a general design concept. 

Optimizing gas transport for C3H6/C3H8 size sieving separation via fine pore engineering of carbon microspheres

Hydrogen carriers are one of the keys to the success of using hydrogen as an energy vector. Indeed, sustainable hydrogen production exploits the excess of renewable energy sources, after which temporary storage is required. The conventional approaches to hydrogen storage and transport are compressed hydrogen (CH2) and liquefied hydrogen (LH2), which require severe operating conditions related to pressure (300–700 bar) and temperature (T &lt; −252 °C), respectively. To overcome these issues, which have hindered market penetration, several alternatives have been proposed in the last few decades. In this review, the most promising hydrogen carriers (ammonia, methanol, liquid organic hydrogen carriers, and metal hydrides) have been considered, and the main stages of their supply chain (production, storage, transportation, H2 release, and their recyclability) have been described and critically analyzed, focusing on the latest results available in the literature, the highlighting of which is our current concern. The last section reviews recent techno-economic analyses to drive the selection of hydrogen carrier systems and the main constraints that must be considered. The analyzed results show how the selection of H2 carriers is a multiparametric function, and it depends on technological factors as well as international policies and regulations. 

Hydrogen Carriers: Scientific Limits and Challenges for the Supply Chain, and Key Factors for Techno-Economic Analysis

This review aims to summarize the recent advancements and prevailing challenges within the realm of hydrogen storage and transportation, thereby providing guidance and impetus for future research and practical applications in this domain. Through a systematic selection and analysis of the latest literature, this study highlights the strengths, limitations, and technological progress of various hydrogen storage methods, including compressed gaseous hydrogen, cryogenic liquid hydrogen, organic liquid hydrogen, and solid material hydrogen storage, as well as the feasibility, efficiency, and infrastructure requirements of different transportation modes such as pipeline, road, and seaborne transportation. The findings reveal that challenges such as low storage density, high costs, and inadequate infrastructure persist despite progress in high-pressure storage and cryogenic liquefaction. This review also underscores the potential of emerging technologies and innovative concepts, including metal–organic frameworks, nanomaterials, and underground storage, along with the potential synergies with renewable energy integration and hydrogen production facilities. In conclusion, interdisciplinary collaboration, policy support, and ongoing research are essential in harnessing hydrogen’s full potential as a clean energy carrier. This review concludes that research in hydrogen storage and transportation is vital to global energy transformation and climate change mitigation. 

A Review of Hydrogen Storage and Transportation: Progresses and Challenges

Nickel-based catalysts are the most promising selection for CO2 methanation. But, it is challenging for monometallic Ni to achieve high CO2 conversion at low temperature. This study develops ceria-supported bimetallic Ni–Ru catalysts that are highly efficient for low-temperature methanation. A small amount of Ru (0.2 wt %) addition to Ni enables the intermetal interaction, and enhances the dispersion of Ni particles with a more active surface, consequently boosting the catalytic capacity for hydrogen activation and CO adsorption. The bimetallic Ni–Ru catalysts exhibit a more than 3-fold rate enhancement at low temperature for selective methanation of CO2 relative to the monometallic Ni/CeO2. Operando IR spectroscopy identifies the formate route as the major reaction mechanism over the monometallic Ni, and the presence of Ru in the bimetallic catalysts can induce the *CO-intermediate mechanistic pathway, contributing to the enhanced production of methane. 

Enhanced Low-Temperature CO2 Methanation over Bimetallic Ni–Ru Catalysts

Olefin/paraffin separation is an important but challenging and energy-intensive process in petrochemical industry. The realization of carbons with size-exclusion capability is highly desirable but rarely reported. Herein, we report polydopamine-derived carbons (PDA-Cx, where x refers to the pyrolysis temperature) with tailorable sub-5 Å micropore orifices together with larger microvoids by one-step pyrolysis. The sub-5 Å micropore orifices centered at 4.1-4.3 Å in PDA-C800 and 3.7-4.0 Å in PDA-C900 allow the entry of olefins while entirely excluding their paraffin counterparts, performing a precise cut-off to discriminate olefin/paraffin with sub-angstrom discrepancy. The larger voids enable high C2H4 and C3H6 capacities of 2.25 and 1.98 mmol g-1 under ambient conditions, respectively. Breakthrough experiments confirm that a one-step adsorption-desorption process can obtain high-purity olefins. Inelastic neutron scattering further reveals the host-guest interaction of adsorbed C2H4 and C3H6 molecules in PDA-Cx. This study opens an avenue to exploit the sub-5 Å micropores in carbon and their desirable size-exclusion effect. 

https://www.nature.com/articles/s41467-023-36890-6.pdf

Probing sub-5 Ångstrom micropores in carbon for precise light olefin/paraffin separation

Hydrogen storage by means of catalytic hydrogenation of suitable organic substrates helps to elevate the volumetric density of hydrogen energy. In this regard, utilizing cheaper industrial crude hydrogen to fulfill the goal of hydrogen storage would show economic attraction. However, because CO impurities in crude hydrogen can easily deactivate metal active sites even in trace amounts such a process has not yet been realized. Here, we develop a robust RuNi/TiO2 catalyst that enables the efficient hydrogenation of toluene to methyl-cyclohexane under simulated crude hydrogen feeds with 1000-5000 ppm CO impurity at around 180 °C under atmospheric pressure. We show that the co-localization of Ru and Ni species during reduction facilitated the formation of tightly coupled metallic Ru-Ni clusters. During the catalytic hydrogenation process, due to the distinct bonding properties, Ru and Ni served as the active sites for CO methanation and toluene hydrogenation respectively. Our work provides fresh insight into the effective utilization and purification of crude hydrogen for the future hydrogen economy. 

/pdf/co-tolerant-runi-tio-2-catalyst-for-the-storage-and-1pimae8i.pdf

CO-tolerant RuNi/TiO_2 catalyst for the storage and purification of crude hydrogen

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Probing sub-5 Ångstrom micropores in carbon for precise light olefin/paraffin separation

CO-tolerant RuNi/TiO_2 catalyst for the storage and purification of crude hydrogen