Research Progress----Shanghai Advanced Research Institute,Chinese Academy of Sciences

Bifunctional Catalysts Enable High para-Xylene Productivity in Syngas Conversion

Recently, a research group from Shanghai Advanced Research Institute (SARI) of the Chinese Academy of Sciences has fabricated bifunctional catalysts combining versatile zeolites and CoMnAl oxide.These catalysts exhibited high stability and high space-time yield of para-xylene under mild reaction conditions.

　　Aromatics, in particular benzene, toluene, and xylenes, are important basic chemicals for highly valuable chemicals and materials.
　　Direct conversion of syngas to aromatics (STA) has drawn much attention and the current reported process can be achieved using tandem catalysts through the methanol or olefin intermediates. However, the development of efficient catalysts with high catalytic activity, selectivity, and stability still remains challenging.
　　Recently, a research group from Shanghai Advanced Research Institute(SARI) of the Chinese Academy of Sciences has fabricated bifunctional catalysts combining versatile zeolites and CoMnAl oxide.
　　These catalysts exhibited high stability and high space-time yield of para-xylene under mild reaction conditions.
　　The study was published in Chem Catalysis on Feb. 14.
　　In order to produce a catalyst capable of converting syngas to aromatics selectively, the researchers first fabricated bifunctional catalysts containing a series of HZSM-5 zeolites and CoMnAl composite oxides (CMA).
　　The combined catalysts were tested in the STA reaction and the distribution of the aromatic products was tuned by modifying the HZSM-5 zeolite with a hollow nanostructure and a silicalite-1 layer grown epitaxially on the HZSM-5 crystals.
　　The results showed that the catalysts comprising CoMnAl catalysts and versatile HZSM-5@silicalite-1 zeolites achieved ultrahigh catalytic activity, selectivity, and stability under mild reaction conditions.
　　The CO conversion surpassed 70% under mild reaction conditions. The selectivity toward aromatics was higher than 63% and the para-xylene fraction of the aromatics produced reached 34.7%. In addition, the catalyst exhibited high stability, with no deactivation was observed over 726 h.
　　Furthermore, the researchers investigated the reaction mechanism and revealed that olefins and oxygen-containing aromatic compounds form were important intermediates inside HSZM-5 during the conversion of syngas to the aromatic products.
　　This study brings enlightenment for high-performance bifunctional catalyst for the direct conversion of syngas to value-added para-xylene. It also improves our understanding of the complex reaction network of syngas to aromatics, paving the way for designing highly active, selective, and stable catalysts for the synthesis of aromatics.
　　
　　Schematic diagram of the syngas to aromatics pathway on CoMnAl/HZSM-5 bifunctional catalysts (Image by SARI)
　　

2022-02-15 more+

New beamlines in trial operation at SSRF

In December 27, four beamlines at the Phase-II project at Shanghai Synchrotron Radiation Facility (SSRF) passed the process test and stared the trail operation, which signified that a total of 11 beamlines and 20 experimental stations have been constructed and put in operation at SSRF.

2021-12-31 more+

Researchers Propose a High-loaded Electrocatalyst with High-efficient Performance Expression in PEMFCs

An interdisciplinary research team led by Prof. YANG Hui and Prof. JIANG Zheng of Shanghai Advanced Research Institute reported a high-loaded (44.7 wt.%) and sub-6 nm Pt IMC catalyst, which can be controllable synthesized through a cobalt oxide aided structural-evolution strategy.

　　Highly-active and durable low-Pt electrocatalysts that can dramatically reduce the costly Pt usage in the oxygen reduction reaction (ORR) are urgently required for the commercialization of fuel cell vehicles. Cost-effective Pt-based intermetallic (IMC) catalysts have been regarded as the most promising alternative to boost activity and durability towards ORR, however, the formation of high-loaded Pt-based IMCs usually involves the high-temperature annealing that leads to severe agglomeration and nonuniformity of IMC nanoparticles (NPs), imposing an enormous challenge on efficient synthesis.
　　Motivated by such a challenge, an interdisciplinary research team led by Prof. YANG Hui and Prof. JIANG Zheng of Shanghai Advanced Research Institute reported a high-loaded (44.7 wt.%) and sub-6 nm Pt IMC catalyst, which can be controllable synthesized through a cobalt oxide aided structural-evolution strategy. The results were published in Energy & Environmental Science recently.
　　The as-prepared catalyst exhibited superb electrocatalytic performance for the ORR with a greatly enhanced mass activity (MA@0.9 V) of 0.53 A mg(Pt)-1 and durability in model electrode measurements.
　　Impressively, the resultant catalyst delivered a record-high power density (2.30/1.23 Wcm-2 for H2-O2/air) and extraordinary stability. Particularly, the MA@0.9 V calculated from fuel cell reaches 0.46 Amg(Pt)-1 in MEA configuration, exceeding the 2020 DOE target (0.44 Amg(Pt)-1 ) and very close to the intrinsic value, indicating that excellent activity can be highly efficient expression under PEMFC operating conditions.
　　The synthetic approach developed in this report provides a feasible strategy for the development of high-loaded, small-sized fuel cell electrocatalysts with high activity expression, paving a new way for future practical application of low-Pt catalysts in fuel cells.
　　Structural feature and electrocatalytic performance of the prepared PtCo-IMC catalysts (Image by Prof. YANG’s group)
　　

2021-12-10 more+

Scientists Propose Novel Bilayer Structure for Crystalline Silicon Solar Cells

Researchers from the Shanghai Advanced Research Institute of the Chinese Academy of Sciences have proposed a novel “bilayer” structure composing of different transition metal oxide (TMO) thin films in crystalline silicon (c-Si) solar cells in order to improve the cells’ efficiency.

　　Researchers from the Shanghai Advanced Research Institute of the Chinese Academy of Sciences have proposed a novel “bilayer” structure composing of different transition metal oxide (TMO) thin films in crystalline silicon (c-Si) solar cells in order to improve the cells’ efficiency.
　　The researchers combined NiOx and MoOx films into a bilayer structure that extracts “hole carriers” from c-Si more efficiently than single-layer films can. The results were published in Cell Reports Physical Science.
　　“Hole carriers” carry a positive charge. Together with electrons, which have opposite polarity, they were created after c-Si absorbs sun light. By extracting positive holes and negative electrons from c-Si to external circuits, the sun light is converted to usable electricity – this is what a c-Si solar cell does. “Extracting” carriers from c-Si is critical and they can be realized by carrier-selective contacts (CSCs) such as TMO films.
　　CSCs play an important role in improving the power conversion efficiency (PCE) of c-Si cells. Existing single-layer, thin TMO films such as MoOx or NiOx cannot effectively extract the desired carriers—mainly holes—thus leading to c-Si solar cells with mediocre efficiency.
　　In a NiOx/MoOx bilayer structure, however, MoOx can induce band bending at the interface, which is favorable for hole carrier extraction. Moreover, NiOx helps to block undesired electron carriers. This is confirmed by both band alignment simulation and minority carrier lifetime measurements.
　　Taking advantages of these features, the researchers reported a remarkable PCE of 21.31% in c-Si solar cells employing NiOx/MoOx bilayers.
　　Moreover, forming an additional ultra-thin SiOx layer on the silicon surface can further suppress loss pathways such as recombination, etc.
　　As a consequence, using an NiOx/SiOx/MoOx structure can further boost the device’s PCE to 21.60%. This is the highest reported efficiency of any c-Si solar cell employing MoOx-based hole-selective contacts instead of a costly a-Si:H passivation layer,according to the researchers.
　　This study highlights a promising and robust approach to employing bilayers as efficient structures for extracting hole carriers. It serves as an inspiring guide for tackling challenges in the field of passivating contact c-Si solar cells.
　　The first author of the publication is LI Le (PhD candidate), the corresponding authors are Dr. ZHANG Shan-Ting and Prof. LI Dongdong. This work was supported by the National Natural Science Foundation of China, the Natural Science Foundation of Shanghai, and the Shanxi Science and Technology Department, among others.
　　
　　Photovoltaic performance of the c-Si solar cells employing NiOx/MoOx bilayer as hole-selective contacts. (Image by SARI)
　　

2021-12-08 more+

Scientists Achieved Direct Conversion of CO2 to a Jet Fuel over CoFe Alloy Catalysts

Direct conversion of carbon dioxide (CO2) using green hydrogen is a sustainable approach to jet fuel production. However, achieving a high level of performance remains a challenge due to the inertness of CO2 and its low activity for subsequent C–C bond formation. a research team led by Prof. Gao Peng, Prof. Li Shenggang and Prof. Sun Yuhan at Shanghai Advanced Research Institute (SARI) reported a Na-modified CoFe alloy catalyst using layered double-hydroxide precursors that directly transforms CO2 to a jet fuel composed of C8-C16 jet-fuel-range hydrocarbons with very high selectivity.

　　The increased consumption of fossil resources is responsible for the emission of large amounts of anthropogenic CO2, which results in climate change and ocean acidification. Direct conversion of carbon dioxide (CO2) using green hydrogen is a sustainable approach to jet fuel production. However, achieving a high level of performance remains a challenge due to the inertness of CO2 and its low activity for subsequent C–C bond formation.
　　Motivated by such a formidable challenge, a research team led by Prof. Gao Peng, Prof. Li Shenggang and Prof. Sun Yuhan at Shanghai Advanced Research Institute (SARI) of the Chinese Academy of Sciences reported a Na-modified CoFe alloy catalyst using layered double-hydroxide precursors that directly transforms CO2 to a jet fuel composed of C8-C16 jet-fuel-range hydrocarbons with very high selectivity. The research results were published in The Innovation entitled "Direct conversion of CO2 to a jet fuel over CoFe alloy catalysts”.
　　The Na-modified CoFe alloy catalyst demonstrates a highly efficient production of jet-fuel-range hydrocarbons with an unprecedentedly high C8-C16 selectivity of 63.5% with 10.2% CO2 conversion as well as a low combined selectivity of less than 22% toward undesired CO and CH4 via direct CO2 hydrogenation (Figure 1).
　　Figure 1. The evaluation data of CO2 hydrogenation over CoFe-0.81Na catalyst. Effects of (A) space velocity and (B) reaction temperature on conversion of CO2, selectivity of CO, and hydrocarbon distribution (Image by SARI)
　　Structural characterization reveals that the Co7Fe3 alloy structure inhibits CH4 formation and plays a crucial role in the selectivity hydrogenation of CO2 to the higher hydrocarbons that constitute jet fuel.
　　The spectroscopic studies suggest that the CoFe alloy surface has a remarkable inhibitory effect on CH4 production via CO2 methantion and the metallic CoFe alloy is the active phase responsible for producing C2+ hydrocarbons from the CO intermediate, whose formation is facilitated by the iron oxide surface sites generated in situ during the CO2 hydrogenation reaction.
　　Density functional theory calculations show that the CoFe catalyst surface has a lower tendency for the C-C coupling reactions than the Co catalyst surface, as reflected from both the calculated energy barriers and reaction energies (Figure 2). This contributes to the narrower carbon distribution from hydrogenation of the CO intermediate over the CoFe catalyst, compared to the Co catalyst.
　　The calculations further show that formation of the CoFe alloy suppresses the CO2 methanation reaction by increasing the energy barrier for the dissociation of the CH3O* intermediate, leading to a lower methane selectivity than that over the Co catalyst. These theoretical predictions are in good agreement with our experimental observations.
　　Figure 2. Density functional theory studies on CO2 hydrogenation to jet fuel. Potential energy profiles of the C-C coupling and CH* hydrogenation over (A) Co and (B) CoFe catalyst surfaces, and (C) of the CH3O* dissociation on Co, CoFe and CoO surfaces. Transition state structures of (D) C-C coupling, (E) CH* hydrogenation, and (F) CH3O* dissociation over the CoFe catalyst surface, and (G) charge density difference of the CH3O* adsorbate over the CoFe catalyst surface. (Image by SARI)
　　This study provides a viable technique for the highly selective synthesis of eco-friendly and carbon-neutral jet fuel from CO2, which can potentially facilitate the rational development of efficient materials for the direct hydrogenation of CO2 to advanced liquid fuels.

2021-11-11 more+

Scientists Reveal the Uniqueness of Ullmann Reaction Path

a research team reported that the Ullmann reaction path is unique regardless of predesigned assembled structures, dominated by the fact that weak intermolecular interaction in assembled nanostructures is suppressed by strong covalent bonding during reactions.

　　On-surface Ullmann coupling has been intensely utilized for the tailor-made fabrication of conjugated frameworks towards molecular electronics, however, reaction mechanisms are still limitedly understood. While manipulating the noncovalent intramolecular interaction and cage effect on surface have been proven to be effective in steering Ullmann coupling reactions, reaction mechanisms are still under intensive investigation nowadays.
　　Motivated by such a challenge, a research team led by Prof. Fei Song at Shanghai Advanced Research Institute (SARI), along with collaborators from Shanghai Institute of Applied Physics, Soochow University, Central South University and Harbin Institute of Technology, reported that the Ullmann reaction path is unique regardless of predesigned assembled structures, dominated by the fact that weak intermolecular interaction in assembled nanostructures is suppressed by strong covalent bonding during reactions. The research results were published in Nano Research entitled "Identifying the convergent reaction path from predesigned assembled structures: Dissymmetrical dehalogenation of Br2Py on Ag(111)”.
　　Surface Ullmann coupling of 2,7-dibromopyrene (Br2Py) on Ag (111) has been elucidated by scanning tunnelling microscopy (STM), X-ray photoelectron, spectroscopy (XPS) and density function theory (DFT). By manipulating deposition conditions, diverse assembled architectures have been constructed for Br2Py on Ag (111). Stepwise annealing leads to an identical reaction diagram for the surface Ullmann coupling from individual assembled structures convergent into the brick-wall-pattern OM dimers first, and then into elongated OM chains in order and eventually long-range polymers with direct C–C coupling. While the reaction mechanism is demonstrated to be dominated by the metal coordinated and halogen bonding motifs, interestingly, it has also been revealed that surface adatoms and dissociated Br atoms play a crucial role in coupling reactions.
　　Although previous reports have claimed that pre-self-assembly strategy can be utilized to steer Ullmann reaction paths and intermediate species, however, for Br2Py on Ag (111) herein, distinct phenomenon is observed while no apparent relationship is found between predesigned nanostructures and reaction path (reactants). Thus, this report proposes essential insights on fundamental understanding of surface Ullmann coupling towards high-yield surface synthesis of functional nanostructures for nono-electronics.
　　Convergent reaction path from diverse assembled structures. (Image by Prof. SONG’s group)

2021-05-25 more+