Ammonia is a promising energy and hydrogen carrier due to its ease of liquification, high hydrogen content, and potential to be synthesized without carbon feedstocks. Despite its widespread use in agriculture, the utilization of ammonia to deliver hydrogen or for direct power generation is still under development. Sometimes referred to as “cracking”, the standard approach for recovering hydrogen from ammonia relies on harsh reaction conditions that limit its suitability for low-carbon transitions. This work investigates the technology development status and potential cost of plasma and electrolysis-based ammonia decomposition, benchmarks them with thermal-chemical decomposition, and further compares them with direct ammonia-to-power solid oxide fuel cell systems. Results suggest that in order to reach cost parity with cracking technologies, plasma-based decomposition must achieve one order of magnitude improvement in energy efficiency (to 10 kWh/kg or lower), while electrolysis decomposition must achieve enhanced durability using cheap electrolytes.

Fischer-Tropsch (F-T) synthesis, converting syngas to hydrocarbons, provides a green alternative for fuel production. Cobalt is one of the most intensively studied F-T catalysts due to its great activity, high stability, and relatively low cost. In this mini review, we summarized some recent advancements in the development of cobalt-based F-T catalysts focusing on the effects of particle size, surface oxidation states, crystallography, and bimetallic particles, with emphasis on the research from our group. Furthermore, non-steady state conditions were investigated to access the initial kinetics using chemical transient kinetics (CTK) experiments, which could bring more insights into the reaction mechanism and catalyst design.

Catalysts development is an evolutionary process. The generation of new single-metal-site catalysts, with isolated metal atoms dispersed on the surface of substrates, offers maximum atom-utilization efficiency, high specific activity, and novel properties. The unique structure of single-site catalysts also enables their potential to bridge the gap between homogeneous and heterogeneous catalysis. This field is at an early stage, characterized by important discoveries and novel demonstrations of catalytic properties associated with the fine structure of single metal sites; however, specific applications, especially catalytic hydrogenation reactions, are still lacking. The focus of this short review is on applications of single-site catalysts in the hydrogen economy based on our studies of hydrogen generation/storage via single-metal-site catalysts. We hope this work will inspire the development of single-site catalysts for other applications.

Single-site catalysts have drawn broad attention in catalysis because of their maximum atomic utilization and unique catalytic performance. Early work in our group has shown a 40-fold higher activity of methanol decomposition over single-site Pt₁/CeO₂ catalyst than CeO₂ supported 2.5 nm Pt nanoparticles, while a molecular-level understanding of such enhancement is lacking. Herein, the reaction mechanism of methanol decomposition over Pt₁/CeO₂ was carefully investigated using in situ DRIFTS, and a reaction pathway was proposed. Methanol molecules were dissociatively adsorbed on nanoceria support first, followed by the diffusion of as-formed methoxy species onto Pt single sites where the dehydrogenation occurs and results in the weakly bonded CO. The ease of methanol dissociative adsorption on nanoceria support and the tailored electronic property of Pt₁ via the metal-support interaction are believed to be strongly correlated with the high activity of Pt₁/CeO₂.

Natural gas (Methane) is currently the primary source of catalytic hydrogen production, accounting for three quarters of the annual global dedicated hydrogen production (about 70 M tons). Steam–methane reforming (SMR) is the currently used industrial process for hydrogen production. However, the SMR process suffers with insufficient catalytic activity, low long-term stability, and excessive energy input, mostly due to the handling of large amount of CO2 coproduced. With the demand for anticipated hydrogen production to reach 122.5 M tons in 2024, novel and upgraded catalytic processes are desired for more effective utilization of precious natural resources. In this review, we summarized the major descriptors of catalyst and reaction engineering of the SMR process and compared the SMR process with its derivative technologies, such as dry reforming with CO2 (DRM), partial oxidation with O2, autothermal reforming with H2 O and O2. Finally, we discussed the new progresses of methane conversion: direct decomposition to hydrogen and solid carbon and selective oxidation in mild conditions to hydrogen containing liquid organics (i.e., methanol, formic acid, and acetic acid), which serve as alternative hydrogen carriers. We hope this review will help to achieve a whole picture of catalytic hydrogen production from methane.

Research evolved using nanoparticles synthesized and characterized under reaction conditions opened the door to study all three fields of catalysis: heterogeneous, homogenous, and enzyme. Fundamental studies of catalytic reactions ranging from hydrogenation to understand Fischer-Tropsch synthesis and isomerization ultimately led to the integration of three fields of catalysis. Our recent work on bridging heterogeneous, homogenous, and enzymatic catalysis was present including functionalization of dendrimer encapsulated metal clusters surface for lactonization, active site engineering in metal organic framework catalysts for methanol production and oligomerization, and single site catalyst for hydrogen production. We envision that the combination of active site engineering and unifying fields of catalysis could be applied to solve practical issues of science-based technology and develop new fields useful in energy research.

Conversion of carbon dioxide to C₂-C₄ hydrocarbons is a major pursuit in clean energy research. Despite tremendous efforts, the lack of well-defined catalysts in which the spatial arrangement of interfaces is precisely controlled hinders the development of more efficient catalysts and in-depth understanding of reaction mechanisms. Herein, we utilized the strategy of tandem catalysis to develop a well-defined nanostructured catalyst CeO₂-Pt@mSiO₂-Co for converting CO₂ to C₂-C₄ hydrocarbons using two metal-oxide interfaces. C₂-C₄ hydrocarbons are found to be produced with high (60%) selectivity, which is speculated to be the result of the two-step tandem process uniquely allowed by this catalyst. Namely, the Pt/CeO₂ interface converts CO₂ and H₂ to CO, and on the neighboring Co/mSiO₂ interface yields C₂-C₄ hydrocarbons through a subsequent Fischer-Tropsch process. In addition, the catalysts show no obvious deactivation over 40 h. The successful production of C₂-C₄ hydrocarbons via a tandem process on a rationally designed, structurally well-defined catalyst demonstrates the power of sophisticated structure control in designing nanostructured catalysts for multiple-step chemical conversions.

The concept of tandem catalysis, where sequential reactions catalyzed by different interfaces in single nanostructure give desirable product selectively, has previously been applied effectively in the production of propanal from methanol (via carbon monoxide and hydrogen) and ethylene via tandem hydroformylation. However, the underlying mechanism leading to enhanced product selectivity has remained elusive due to the lack of stable, well-defined catalyst suitable for in-depth comprehensive study. Accordingly, we present the design and synthesis of a three-dimensional (3D) catalyst CeO2-Pt@mSiO2 with well-defined metal-oxide interfaces and stable architecture and investigate the selective conversion of ethylene to propanal via tandem hydroformylation. The effective production of aldehyde through the tandem hydroformylation was also observed on propylene and 1-butene. A thorough study of the CeO2-Pt@mSiO2 under different reaction and control conditions reveals that the ethylene present for the hydroformylation step slows down initial methanol decomposition, preventing the accumulation of hydrogen (H2) and favoring propanal formation to achieve up to 80% selectivity. The selectivity is also promoted by the fact that the reaction intermediates produced from methanol decomposition are poised to directly undergo hydroformylation upon migration from one catalytic interface to another. This synergistic effect between the two sequential reactions and the corresponding altered reaction pathway, compared to the single-step reaction, constitute the key advantages of this tandem catalysis. Ultimately, this in-depth study unravels the principles of tandem catalysis related to hydroformylation and represents a key step toward the rational design of new heterogeneous catalysts.