10 Search Results

Efficient catalysts for the dehydrogenation and hydrogenation of liquid organic hydrogen carriers (LOHCs) are essential for advancing hydrogen storage and transportation. Conventional nanoparticle catalysts suffer from low metal utilization, while single-atom catalysts (SAC) are limited by isolated active sites. Here, in this work, we present a hetero duo-atomic catalyst, Pt₁–Ga₁/CeO₂ DAC, which exhibits exceptional activity, selectivity, stability, and recyclability for N-heterocycle hydrogen storage. Ga plays a critical role in C–H bond activation, acting as a mediator in catalytic bond-breaking and formation. Compared with Pt₁/CeO₂ SAC, Pt₁–Ga₁/CeO₂ DAC enhances metal utilization while overcoming SAC limitations for large substrates. This work establishesmore » a promising strategy for designing highly efficient catalysts for LOHC applications.« less

Abstract Developing highly efficient and reversible hydrogenation-dehydrogenation catalysts shows great promise for hydrogen storage technologies with highly desirable economic and ecological benefits. Herein, we show that reaction sites consisting of single Pt atoms and neighboring oxygen vacancies (V _O ) can be prepared on CeO ₂ (Pt ₁ /CeO ₂ ) with unique catalytic properties for the reversible dehydrogenation and rehydrogenation of large molecules such as cyclohexane and methylcyclohexane. Specifically, we find that the dehydrogenation rate of cyclohexane and methylcyclohexane on such sites can reach values above 32,000 mol _H2 mol _Pt ⁻¹ h ⁻¹ , which is 309 timesmore » higher than that of conventional supported Pt nanoparticles. Combining of DRIFTS, AP-XPS, EXAFS, and DFT calculations, we show that the Pt ₁ /CeO ₂ catalyst exhibits a super-synergistic effect between the catalytic Pt atom and its support, involving redox coupling between Pt and Ce ions, enabling adsorption, activation and reaction of large molecules with sufficient versatility to drive abstraction/addition of hydrogen without requiring multiple reaction sites.« less

We demonstrated how the special synergy between a noble metal single site and neighboring oxygen vacancies provides an "ensemble reaction pool" for high hydrogen generation efficiency and carbon dioxide (CO₂) selectivity of a tandem reaction: methanol steam reforming. Specifically, the hydrogen generation rate over single site Ru₁/CeO₂ catalyst is up to 9360 mol H₂ per mol Ru per hour (579 mL_H2 g_Ru^-1 s^-1) with 99.5% CO₂ selectivity. Reaction mechanism study showed that the integration of metal single site and O vacancies facilitated the tandem reaction, which consisted of methanol dehydrogenation, water dissociation, and the subsequent water gas shift (WGS) reaction. In addition,more » the strength of CO adsorption and the reaction activation energy difference between methanol dehydrogenation and WGS reaction play an important role in determining the activity and CO₂ selectivity. Our study paves the way for the further rational design of single site catalysts at the atomic scale. Furthermore, the development of such highly efficient and selective hydrogen evolution systems promises to deliver highly desirable economic and ecological benefits.« less

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 andmore » 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.« less

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. Here, we focus on applications of single-site catalysts in the hydrogen economy basedmore » 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.« less

Liquid organic hydrogen carriers such as alcohols and polyols are a high-capacity means of transporting and reversibly storing hydrogen that demands effective catalysts to drive the (de)hydrogenation reactions under mild conditions. We employed a combined theory/experiment approach to develop MOF-74 catalysts for alcohol dehydrogenation and examine the performance of the open metal sites (OMS), which have properties analogous to the active sites in high-performance single-site catalysts and homogeneous catalysts. Methanol dehydrogenation was used as a model reaction system for assessing the performance of five monometallic M-MOF-74 variants (M = Co, Cu, Mg, Mn, Ni). Co-MOF-74 and Ni-MOF-74 give the highestmore » H₂ productivity. However, Ni-MOF-74 is unstable under reaction conditions and forms metallic nickel particles. To improve catalyst activity and stability, bimetallic (NixMg_1-x)-MOF-74 catalysts were developed that stabilize the Ni OMS and promote the dehydrogenation reaction. An optimal composition exists at (Ni_0.32Mg_0.68)-MOF-74 that gives the greatest H2 productivity, up to 203 mL gcat^-1 min^-1 at 300 °C, and maintains 100% selectivity to CO and H₂ between 225–275 °C. The optimized catalyst is also active for the dehydrogenation of other alcohols. DFT calculations reveal that synergistic interactions between the open metal site and the organic linker lead to lower reaction barriers in the MOF catalysts compared to the open metal site alone. This work expands the suite of hydrogen-related reactions catalyzed by MOF-74 which includes recent work on hydroformulation and our earlier reports of aryl-ether hydrogenolysis. Moreover, it highlights the use of bimetallic frameworks as an effective strategy for stabilizing a high density of catalytically active open metal sites.« less

We demonstrate that the single-site catalyst Pt₁/CeO₂ greatly enhances the selectivity of cyclization and aromatization in the n-hexane reforming reaction. Specifically, the selectivity of single-site Pt₁/CeO₂ toward both cyclization and aromatization is above 86% at 350 °C. The turnover frequency of Pt₁/CeO₂ is 58.8 h^-1 at 400 °C, which is close to that of Pt cluster/CeO₂ (61.4 h^-1) and much higher than that of Pt nanoparticle/CeO₂ with Pt sizes of 2.5 and 7 nm. On the basis of the catalytic results for methylcyclopentane reforming, the dehydrocyclization and further aromatization of n-hexane are attributed to the prominent adsorption of ring intermediatemore » products on the single-site Pt₁/CeO₂ catalysts. On the other side, with the multiple Pt adjacent active sites, the cluster and nanoparticle Pt/CeO₂ samples favor the C-C bond cracking reaction. Ultimately, this in-depth study unravels the principles of hydrocarbon activation with different Pt sizes and represents a key step toward the rational design of new heterogeneous catalysts.« less

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 summarizedmore » 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 H₂O 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.« less

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. Overall, 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 mechanismmore » and catalyst design.« less

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 andmore » unifying fields of catalysis could be applied to solve practical issues of science-based technology and develop new fields useful in energy research.« less