A strong bimetal-support interaction in ethanol steam reforming

Concerted catalysis of single atom and nanocluster enhances bio-ethanol activation and dehydrogenation

Single atom and nanocluster catalysts are extensively investigated in heterogeneous catalysis due to their high catalytic activity and atomic utilization, while their coexisting properties and potentially synergistic effect are yet to be clarified. Herein, we construct three systems of atomic-scale catalysts (xNi/Mo2TiAlC2, x = 0.5, 1, and 1.5) for bio-ethanol reforming, which correspond to single atoms, single atoms mixed with nanoclusters, and nanoclusters. The respective hydrogen utilization efficiency of mixed-form catalyst increases by 43.7% and 29.3% compared to single atom and nanocluster catalysts. Results demonstrate that the adjacent Ni single atom facilitates electron transfer from Mo2TiAlC2 to Ni-Mo interface and raises the d-band center, thus enhancing bio-ethanol adsorption and activation; while the existence of Ni nanoclusters contributes to lowering the energy barriers of CH3CHO* dehydrogenation. The catalytically active sites are Ni-Mo alloyed single atoms with adjacent Ni nanoclusters. This work provides new implications for highly activated catalytic site construction and advanced catalyst design.

Promoting C-F Bond Activation for Perfluorinated Compounds Decomposition via Atomically Synergistic Lewis and Brønsted Acid Sites

Catalytic hydrolysis is a sustainable method for the degradation of perfluorinated compounds (PFCs) but is challenged by the high reaction temperatures required to cleave strong C-F bonds. Herein, we developed an innovative C-F activation strategy by constructing synergistic Lewis and Brønsted acid pairs over atomically dispersed Zn-O-Al sites to promote C-F bond activation for decomposition of typical PFCs, CF4. Density functional theory (DFT) calculations demonstrate tricoordinated Al (AlIII) sites and Zn-OH functional, respectively, as Lewis and Brønsted acid sites over Zn-O-Al, synergistically enhancing the adsorption and decomposition of CF4. X-ray absorption spectroscopy (XAS), pyridine infrared spectroscopy (Py-IR), and ammonia temperature-programmed desorption (NH3-TPD) verified the presence of both AlIII and Zn-OH on the atomically dispersed Zn-O-Al sites. CF4-TPD and in situ infrared spectroscopy confirmed that the Zn-O-Al sites facilitate CF4 adsorption and C-F bond activation. As a result, the Zn-O-Al sites with synergistic Lewis and Brønsted acid pairs achieved 100% CF4 decomposition at a low temperature of 560 °C and demonstrated outstanding stability for more than 250 h.

Oxygen Vacancies Promote Formaldehyde Base-Free Reforming into Hydrogen over Cu Doping-Induced Cu-CuxZn1-xO Heterointerfaces

Element doping is a viable strategy to regulate the metal-support interface for enhancing the catalytic performance of supported metal catalysts. Herein, Cu/ZnO:Cu-TH catalysts are prepared by immobilizing Cu nanoparticles (NPs) on ZnO nanorods featuring an adjustable oxygen vacancy, in which partial Cu atoms at the Cu-ZnO interface are incorporated into the ZnO lattice to form CuxZn1-xO species. Such Cu atom doping induces the creation of distinctive Cu-CuxZn1-xO interface sites and optimizes electron transfer from ZnO to Cu NPs, thereby achieving intermediate activation and ultimately endowing the catalyst with superior performance in reforming alkali-free formaldehyde (HCHO) into hydrogen at low temperatures. The Cu-CuxZn1-xO interface sites serve as pivotal centers for HCHO reforming, where the Cu sites and CuxZn1-xO sites selectively engage in the cleavage of C-H bonds in HCHO and O-H bonds in H2O, respectively. Meanwhile, the presence of oxygen vacancies bolsters the Cu-CuxZn1-xO sites in enhancing the adsorption of HCHO and H2O, further improving the activity. The Cu/ZnO:Cu-450H catalyst, distinguished by abundant Cu-CuxZn1-xO sites and a high concentration of oxygen vacancies, demonstrates optimal activity with TOF values of 16.9 and 72.4 h-1 under anaerobic and aerobic conditions, respectively, which are 8.9 and 29.0 times higher than those of the Cu/ZnO-450N catalyst, which lacks doped Cu atoms and oxygen vacancies.

Optimizing selectivity via steering dominant reaction mechanisms in steam reforming of methanol for hydrogen production

Enhancing selectivity towards specific products remains a pivotal challenge in energy catalysis. Herein, we present a strategy to refine selectivity via pathway optimization, exemplified by the rational design of catalysts for methanol steam reforming. Over traditional Pd/ZnO catalysts, the direct decomposition of key intermediates CH2O* into CO and H2 on PdZn alloys competes with the oxidation of CH2O* to CO2, leading to inferior selectivity in product distribution. To address this challenge, Cu is introduced to modify the catalytic dynamics, lowering the dissociation energy barrier of water to provide more active hydroxyl groups for the oxidation of CH2O*. Simultaneously, the CO desorption energy barrier on PdCu alloys is elevated, thereby hindering CH2O* decomposition. This dual functionality enhances both the selectivity and activity of the methanol steam reforming reaction. By modulating the activation patterns of key intermediate species, this approach provides new insights into catalyst design for improved reaction selectivity.

Plasma-Catalyst Dynamics: Nonthermal Activation of Strong Metal-Support Interactions

Nonthermal plasma-surface interactions enable transformative advancements in green chemistry, healthcare, materials processing, pollution abatement, and the ever-growing area of plasma catalysis. In the context of plasma catalysis, the fate of the active sites during plasma treatment has remained enigmatic, and observation of low-temperature plasma-catalyst events has been challenging. The induction of strong metal-support interactions (SMSI) through high-temperature hydrogen treatment is a well-documented and established, yet limited, method to impact selectivity and stability of noble metal catalysts on reducible supports. Thermally driven SMSI occurs through reduction and subsequent migration of the support to the surface of exposed metal sites, thus affecting the catalyst both electronically and geometrically and serving as an ideal system to evaluate dynamic plasma-catalyst interactions. In this study, a dielectric barrier discharge of hydrogen was used to successfully induce a plasma-SMSI state (P-SMSI) in niobia-supported platinum particles at bulk-gas temperatures as low as -30 °C, which enhances the selectivity for propane dehydrogenation and offers conclusive evidence of plasma-catalyst interactions. Time-resolved spectroscopic evidence of this phenomenon was obtained in situ using a cryogenically cooled plasma IR transmission cell, which provided evidence of diffusion-controlled surface migration. Collectively, P-SMSI constitutes a promising, low-impact technology for synthesizing SMSI-enhanced catalysts with controllable active sites, and knowledge of the nonthermal plasma-catalyst dynamics is critical in designing materials for specific applications or selecting conditions of operation.

Pr doping promotes the formation of Pt single atoms by regulating metal-support interaction for remarkable photocatalytic hydrogen production

Since the metal-support interaction (MSI) has a great influence on the structure and properties of single atom catalysts (SACs), the activity and stability of SACs can be effectively regulated by adjusting the structure of the matrix. Herein, the morphology of surface supported Pt species can be controlled by doping to adjust the properties of TiO2 support. Specifically, under the same conditions, the Pt species on the Pr doped TiO2 surface are Pt SAs (PtSA/TiO2(Pr)), while on the pure TiO2 surface are particles (PtNP/TiO2). Experimental and theoretical studies demonstrate that Pr doping weakens the interaction of Ti-O bond, stabilizes the O-Pt unit site and Pt SAs. Impressively, PtSA/TiO2(Pr) shows superior photocatalytic hydrogen production performance (196.43 mmol g-1 h-1), far exceeding PtNP/TiO2 (91.96 mmol g-1 h-1). Additionally, Pr dopant modulates the electronic interaction between TiO2 support and Pt SAs, thus the adsorption/desorption behavior of H intermediates (H*) is balanced. Besides, the electron delocalization of O adjacent to Pt SAs can be adjusted by Pr doping, prompting the establishment of efficient Pt-O electron transfer channels and further enhances the utilization of photogenerated carriers. This study presents a promising strategy to prepare SACs with high activity for photocatalyst hydrogen production.

Covalent Organic Frameworks for Electrocatalysis: Design, Applications, and Perspectives

Covalent organic frameworks (COFs) are an innovative class of crystalline porous polymers composed of light elements such as C, N, O, etc., linked by covalent bonds. The distinctive properties of COFs, including designable building blocks, large specific surface area, tunable pore size, abundant active sites, and remarkable stability, have led their widespread applications in electrocatalysis. In recent years, COF-based electrocatalysts have made remarkable progress in various electrocatalytic fields, including the hydrogen evolution reaction, oxygen evolution reaction, oxygen reduction reaction, nitrogen reduction reaction, nitrate reduction reaction, and carbon dioxide reduction reaction. This review begins with an introduction to the design and synthesis strategies employed for COF-based electrocatalysts. These strategies include heteroatom doping, metalation of COF and building monomers, encapsulation of active sites within COF pores, and the development of COF-based derived materials. Subsequently, a systematic overview of the recent advancements in the application of COF-based catalysts in electrocatalysis is presented. Finally, the review discusses the main challenges and outlines possible avenues for the future development of COF-based electrocatalysts.

Solar-Driven Biomass Reforming for Hydrogen Generation: Principles, Advances, and Challenges

Hydrogen (H2) has emerged as a clean and versatile energy carrier to power a carbon-neutral economy for the post-fossil era. Hydrogen generation from low-cost and renewable biomass by virtually inexhaustible solar energy presents an innovative strategy to process organic solid waste, combat the energy crisis, and achieve carbon neutrality. Herein, the progress and breakthroughs in solar-powered H2 production from biomass are reviewed. The basic principles of solar-driven H2 generation from biomass are first introduced for a better understanding of the reaction mechanism. Next, the merits and shortcomings of various semiconductors and cocatalysts are summarized, and the strategies for addressing the related issues are also elaborated. Then, various bio-based feedstocks for solar-driven H2 production are reviewed with an emphasis on the effect of photocatalysts and catalytic systems on performance. Of note, the concurrent generation of value-added chemicals from biomass reforming is emphasized as well. Meanwhile, the emerging photo-thermal coupling strategy that shows a grand prospect for maximally utilizing the entire solar energy spectrum is also discussed. Further, the direct utilization of hydrogen from biomass as a green reductant for producing value-added chemicals via organic reactions is also highlighted. Finally, the challenges and perspectives of photoreforming biomass toward hydrogen are envisioned.

Changeable Active Sites by Pr Doping CuSA-TiO2 Photocatalyst for Excellent Hydrogen Production

Photocatalytic water splitting for clean hydrogen production has been a very attractive research field for decades. However, the insightful understanding of the actual active sites and their impact on catalytic performance is still ambiguous. Herein, a Pr-doped TiO2-supported Cu single atom (SA) photocatalyst is successfully synthesized (noted as Cu/Pr-TiO2). It is found that Pr dopants passivate the formation of oxygen vacancies, promoting the density of photogenerated electrons on the CuSAs, and optimizing the electronic structure and H* adsorption behavior on the CuSA active sites. The photocatalytic hydrogen evolution rate of the obtained Cu/Pr-TiO2 catalyst reaches 32.88 mmol g-1 h-1, 2.3 times higher than the Cu/TiO2. Innovatively, the excellent catalytic activity and performance is attributed to the active sites change from O atoms to CuSAs after Pr doping is found. This work provides new insight for understanding the accurate roles of single atoms in photocatalytic water splitting.

Hydrogen Production through Distinctive C-C Cleavage during Acetic Acid Reforming at Low Temperature

Acetic acid reforming is a green method for sustainable hydrogen production owing to its renewable source from biomass conversion. However, conventional acetic acid reforming would produce various byproducts, including CO, CH4 and so on. Here, we develop a distinctive method for selective hydrogen production from C-C directional cleavage during acetic acid reforming. Completely different from conventional acetic acid reforming process, acetic acid would react with water over organoruthenium catalyst during its C-C cleavage at low temperature, then produce methanol and formic acid (CH3COOH+H2O→CH3OH+HCOOH). Lastly, methanol and formic acid could further decompose into hydrogen and carbon dioxide over organoruthenium selectively. As a result, there is little CO and CH4 produced in the first step of C-C bond cleavage during acetic acid reforming at 100 °C. Hydrogen production rate is up to 26.8 molH2/(h-1*mol-1 Ru) at 150 °C through a tandem catalysis. A mechanism for C-C cleavage of acetic acid is proposed based on intermediate product analysis and density functional theory (DFT) calculation. Firstly, the C-C single bond was transformed into C=C double bond by dropping one H atom to organoruthenium. Then the coming H2O molecule reacted with the C=C bond by an addition reaction, forming methanol and formic acid. This research not only proposes distinctive reaction pathway for hydrogen production from acetic acid reforming, but also provides some inspiration for selective C-C bond cleavage during ethanol reforming.

Facilitating the dry reforming of methane with interfacial synergistic catalysis in an Ir@CeO2-x catalyst

The dry reforming of methane provides an attractive route to convert greenhouse gases (CH4 and CO2) into valuable syngas, so as to resolve the carbon cycle and environmental issues. However, the development of high-performance catalysts remains a huge challenge. Herein, we report a 0.6% Ir/CeO2-x catalyst with a metal-support interface structure which exhibits high CH4 (~72%) and CO2 (~82%) conversion and a CH4 reaction rate of ~973 μmolCH4 gcat-1 s-1 which is stable over 100 h at 700 °C. The performance of the catalyst is close to the state-of-the-art in this area of research. A combination of in situ spectroscopic characterization and theoretical calculations highlight the importance of the interfacial structure as an intrinsic active center to facilitate the CH4 dissociation (the rate-determining step) and the CH2* oxidation to CH2O* without coke formation, which accounts for the long-term stability. The catalyst in this work has a potential application prospect in the field of high-value utilization of carbon resources.

Air-Promoted Light-Driven Hydrogen Production from Bioethanol over Core/Shell Cr2O3@GaN Nanoarchitecture

Light-driven hydrogen production from biomass derivatives offers a path towards carbon neutrality. It is often however operated with the limitations of sluggish kinetics and severe coking. Herein, a disruptive air-promoted strategy is explored for efficient and durable light-driven hydrogen production from ethanol over a core/shell Cr2O3@GaN nanoarchitecture. The correlative computational and experimental investigations show ethanol is energetically favorable to be adsorbed on the Cr2O3@GaN interface, followed by dehydrogenation toward acetaldehyde and protons by photoexcited holes. The released protons are then consumed for H2 evolution by photogenerated electrons. Afterward, O2 can be evolved into active oxygen species and promote the deprotonation and C-C cleavage of the key C2 intermediate, thus significantly lowering the reaction energy barrier of hydrogen evolution and removing the carbon residual with inhibited overoxidation. Consequently, hydrogen is produced at a high rate of 76.9 mole H2 per gram Cr2O3@GaN per hour by only feeding ethanol, air, and light, leading to the achievement of a turnover number of 266,943,000 mole H2 per mole Cr2O3 over a long-term operation of 180 hours. Notably, an unprecedented light-to-hydrogen efficiency of 17.6 % is achieved under concentrated light illumination. The simultaneous generation of aldehyde from ethanol dehydrogenation enables the process more economically promising.

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

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.

Constructing Symmetry-Mismatched RuxFe3-xO4 Heterointerface-Supported Ru Clusters for Efficient Hydrogen Evolution and Oxidation Reactions

Ru-related catalysts have shown excellent performance for the hydrogen evolution reaction (HER) and hydrogen oxidation reaction (HOR); however, a deep understanding of Ru-active sites on a nanoscale heterogeneous support for hydrogen catalysis is still lacking. Herein, a click chemistry strategy is proposed to design Ru cluster-decorated nanometer RuxFe3-xO4 heterointerfaces (Ru/RuxFe3-xO4) as highly effective bifunctional hydrogen catalysts. It is found that introducing Ru into nanometric Fe3O4 species breaks the symmetry configuration and optimizes the active site in Ru/RuxFe3-xO4 for HER and HOR. As expected, the catalyst displays prominent alkaline HER and HOR performance with mass activity much higher than that of commercial Pt/C as well as robust stability during catalysis because of the strong interaction between the Ru cluster and the RuxFe3-xO4 support, and the optimized adsorption intermediate (Had and OHad). This work sheds light on a promsing approach to improving the electrocatalysis performance of catalysts by the breaking of atomic dimension symmetry.

Investigation of Ni-Cu-acid multifunctional synergism in NiCu-phyllosilicate catalysts toward the 1,4-butynediol hydrogenation to 1,4-butanediol

We studied the Ni-Cu-acid multifunctional synergism in NiCu-phyllosilicate catalysts toward 1,4-butynediol hydrogenation to 1,4-butanediol by varying the reduction temperature, which can activate different bimetal and support interactions. Compared with a monometallic Ni phyllosilicate (phy), which only showed one type of metal species when reduced at ∼750 °C, there are three types of metal species for the bimetallic Ni-Cu-phyllosilicate derived catalysts, namely Cuphy, differentiated Ni, and Niphy. Thorough structure-activity/selectivity correlation investigations showed that, although the Ni9Cu1-P catalyst matrix can produce tiny amounts of differentiated Ni0 species under the induction of reduced Cu0 at R250 condition, it could not form Ni-Cu bimetallic interactions for the collaborative hydrogenation of 1,4-butynediol, and the product stays in the semi hydrogenated state. When the reduction temperature is raised to 500 °C, stable Ni-Cu alloy active sites exist, accompanied by the strong metal support interaction and metal acid effect derived from the intimate contact between the extracted metal sites and the surviving functional phyllosilicate support; these functionalities yield a supreme hydrogenation performance of the R500 sample with a 1,4-butanediol yield larger than 91.2%.

Fabrication of highly dispersed Pd-Mn3O4 catalyst for efficient catalytic propane total oxidation

Adjusting the interaction between dual active components for enhancing volatile organic compounds (VOCs) degradation is an effective but still challenging means of air pollution control. Herein, a limited pyrolysis oxidation strategy was adopted to prepare Pd-Mn3O4 spinel catalysts with uniform morphology and active component dispersion. Among these, 1.08Pd-Mn3O4 presented the highest catalytic efficiency with a T90 value of 240 °C, which was 94 °C lower than that of Mn3O4. Characterization and density functional theory (DFT) calculation results revealed that the strong metal-support interaction (SMSI) effect between Pd and Mn3O4 promoted the redistribution of surface charges, thus strengthening the oxidation-reduction ability of the active sites. Moreover, the SMSI effect led to a better migration of surface oxygen species, and boosted the generation of active surface oxygen species. Simultaneously, the Pd catalyst further reduced the energy barrier in the initial stage of the dehydrogenation of propane. Overall, this study provided a novel design strategy for dual active components catalysts with SMSI effect and extended the application of these catalysts in the important field of VOCs elimination.

A mini review on recent progress of steam reforming of ethanol

H2 is one of the promising renewable energy sources, but its production and transportation remain challenging. Distributed H2 production using liquid H2 carriers is one of the ideal ways of H2 utilization. Among common H2 carriers, ethanol is promising as it has high H2 content and can be derived from renewable bio-energy sources such as sucrose, starch compounds, and cellulosic biomass. To generate H2 from ethanol, steam reforming of ethanol (SRE) is the most common way, while appropriate catalysts, usually supported metal catalysts, are indispensable. However, the SRE process is quite complicated and always accompanied by various undesirable by-products, causing low H2 yield. Moreover, the catalysts for SRE are easy to deactivate due to sintering and carbon deposition under high reaction temperatures. In recent years, lots of efforts have been made to reveal SRE mechanisms and synthesize catalysts with high H2 yield and excellent stability. Both active metals and supports play an important role in the reaction. This mini-review summarizes the recent progress of SRE catalysts from the view of the impacts of active metals and supports and draws an outlook for future research directions.