Academician Nanfeng Zheng’s Research Team at Xiamen University, JACS: Ou Shisheng Catalyst Evaluation System Facilitates Direct Aromatic Hydrogenation for Hydrogen Storage Using Crude Hydrogen
A recent paper in JACS, titled "Achieving Distributed and Flexible Hydrogenation of Aromatics with Crude Hydrogen from Electrolyzers" details research by Academician Nanfeng Zheng ’s group at Xiamen University. The study focused on distributed and flexible aromatic hydrogenation and green hydrogen storage, utilizing crude hydrogen from electrolyzers. Ou Shisheng (Beijing) Technology Co., Ltd. (Ou Shisheng) provided its EMC-3 series fully automatic catalyst evaluation system for this research. This system was utilized to assess the long-term stability of aromatic hydrogenation catalysts under continuous-flow conditions.
Automatic Catalyst Evaluation Device from Ou Shisheng
Features of the OSSKJ Automatic Catalyst Evaluation Device
· Rapid Equilibration: Features a microchannel gas-liquid mixer for thorough mixing in a μL volume, achieving system pressure within 2 seconds.
· Precise Liquid Level Measurement: A tolerance-type liquid level sensor automatically detects the liquid surface with an accuracy of ±0.1 mL.
· Stable Pressure and Liquid Control: Offers pressure control accuracy up to 0.1 MPa. A flow stabilizing valve automatically adjusts its opening based on the liquid level, ensuring continuous and steady outflow of liquid products.
· Real-Time Product Sampling: Allows for timed or fixed-volume product sampling. An integrated optical probe effectively eliminates bubble interference.
· Scalable Throughput: Throughput can be expanded as needed for experimental requirements, supporting a maximum of 32 channels.
Paper Highlights
Paper：Achieving Distributed and Flexible Hydrogenation of Aromatics with Crude Hydrogen from Electrolyzers，J. Am. Chem. Soc. 2026，DOI: 10.1021/jacs.6c09601
Authors: Research group of Academician Nanfeng Zheng . Corresponding authors: Nanfeng Zheng , Ruixuan Qin , HuabingTao and Xiankui Wei .
Key Conclusions: Au–Pt bimetallic catalysts with platinum-enriched surfaces were created using "Pt ensemble engineering." These catalysts efficiently perform aromatic hydrogenation under mild conditions and enable distributed, flexible hydrogen storage directly from crude hydrogen produced by photovoltaic-PEM electrolysis.
I. The Bottleneck for "Green Hydrogen in the Chemical Industry" is the Hydrogenation Step
The primary obstacle to the widespread use of green hydrogen in industry is not its production, but its storage. Storing hydrogen in liquid organic hydrogen carriers (LOHCs) is currently one of the most practical methods. However, the aromatic hydrogenation step for hydrogen storage has traditionally required temperatures above 100 °C and pure hydrogen at several MPa. These demanding conditions make direct integration with crude hydrogen from electrolyzers challenging, as this hydrogen contains water, is at low pressure, and fluctuates with weather conditions.
Three major challenges persist:
First, aromatic rings are chemically stable, and hydrogenation necessitates overcoming a significant energy barrier.
Second, aromatic molecules and H₂ compete for the same active sites on the catalyst surface. If the sites bind aromatics too strongly, it hinders product desorption. Conversely, if the binding is too weak, H₂ cannot be dissociated and activated. Therefore, precisely tuning the co-adsorption energies of both species is crucial.
Third, fluctuating hydrogen flow can cause irreversible surface reconstruction and deactivation of catalysts designed for steady-state operation. Yet, hydrogen storage applications require catalysts to perform stably over long periods despite intermittent hydrogen supply.
II. Breakthrough: Pt Ensemble Engineering and Its Experimental Performance
To tackle the aforementioned challenges, the Xiamen University team departed from conventional strategies such as increasing noble metal loading or switching support materials. Instead, the research focused on tuning the geometric dimension of active sites and proposed Pt ensemble engineering: constructing size-precisely controllable Pt ensembles on Au surfaces. By adjusting the number of atoms within each ensemble, the co-adsorption energies of aromatic rings and hydrogen can be modulated.
The team synthesized a series of bimetallic colloidal nanoparticles of PtₓAu₁₀₋ₓ (x = 0, 1, 3, 5, 7, 10) with particle sizes of approximately 6–7 nm. These nanoparticles were supported on TiO₂ and evaluated for benzoic acid hydrogenation under mild conditions.
Experimental results show a tenfold increase in catalytic performance. At 60 °C and 1 bar of H₂, the Pt₃Au₇/TiO₂ catalyst achieves a turnover frequency (TOF) of 5250 h⁻¹. This significantly surpasses previously reported catalysts tested under atmospheric H₂, exceeding them by more than a factor of ten. It also outperforms the best catalysts operating at 10–50 bar and higher temperatures. The catalytic activity displays a volcanic trend with increasing Pt content, with the experimental activity ranking as follows: Pt₃Au₇ > Pt₅Au₅ > Pt₇Au₃ > Pt. Considering both mass-specific activity and the amount of noble metal used, the researchers selected Pt₅Au₅ for further mechanistic studies and scale-up investigations.
This selected catalyst demonstrates a wide range of substrate applicability. It efficiently hydrogenates various aromatic carboxylic acids, phenols, ethers, esters, dimethyl terephthalate (a precursor for CHDM and CHDA polymer monomers), fluorobenzene, LOHC substrates, nitrogen-containing heterocycles, and aromatic amides. The paper also notes the catalyst's limitations, stating that no significant hydrogenation of naphthalene, ethylcarbazole, aniline, p-phenylenediamine, or sulfur-containing aromatics was observed under mild conditions.
Regarding cyclic stability, under pure hydrogen, the conversion of benzoic acid decreased from 98% to 25% after three cycles. However, after air treatment at 400 °C, the catalyst maintained stable activity and selectivity over the following five cycles.
Figure 1｜(a) Representative HAADF-STEM image of Pt₃Au₇ nanoparticles; (b–e) STEM-EDX elemental mapping of Pt₃Au₇; (f) TOF values of various PtₓAu₁₀₋ₓ/TiO₂ catalysts; (g) Comparison of TOF between Pt₃Au₇/TiO₂ and previously reported catalysts, where the bubble size represents the TOF value.
III. Mechanism and Validation: Substrate Anchoring Stabilization
DFT calculations show that the ensemble size is critical: benzoic acid adsorbs significantly only when four adjacent Pt sites are present on the surface. When the ensemble comprises exactly five Pt atoms, benzoic acid occupies four of these sites, leaving one site available for the co-adsorption and activation of H₂. This lowers the hydrogenation barrier from 1.94 eV (observed with Pt₁Au using the Eley–Rideal pathway) to 0.80 or 0.85 eV. This barrier is even lower than that on the Pt(111) surface. A typical volcanic trend exists between ensemble size and the effective barrier, indicating that neither excessively large nor too small Pt ensembles are optimal for the synergistic activation of aromatic rings and hydrogen.
Figure 4 (a–c)｜(a) Top-view models of Pt ensembles with different sizes constructed on the Au(111) surface; (b) Energy profile for stepwise hydrogenation of benzoic acid; (c) Volcanic relationship between effective reaction barrier and the co-adsorption energies of benzoic acid / H₂.
Building on these findings, the team discovered that aromatic substrates can stabilize the surface structure of catalytic active sites. Ab initio molecular dynamics (AIMD) simulations show that when toluene adsorbs onto Pt sites, the average Pt–Au coordination number remains stable at about 5.17, and the Pt atoms stay on the surface. However, without toluene present, Pt atoms tend to migrate into the bulk phase, increasing the coordination number to 6.02.
In-situ X-ray absorption spectroscopy (XAS) offers supporting evidence. Under a pure H₂ atmosphere, the Pt–(Pt/Au) bond length increases from 2.741 Å to 2.752 Å, indicating surface reconstruction induced by hydrogen. When both toluene and H₂ are present, the bond length returns to 2.736 Å, close to its initial state. The researchers termed this mechanism “substrate-anchored stabilization.”
It is important to note that simulations are limited to the ps timescale and cannot fully capture the long-term behavior of catalysts during operation. The paper clarifies that these simulations are used to identify major structural trends, while “the long-term evolution of working catalysts finds its engineering counterpart in the continuous-flow experiments described below.”
The validation was performed using the Ou Shisheng EMC-3 series automatic catalyst evaluation system.
Packing: The catalyst was mixed with quartz sand and packed into a 6 mm inner diameter stainless steel reaction column.
Feed: Hydrogen (H₂) and toluene were delivered at set flow rates, and the system was maintained at the target pressure.
Temperature: The reaction was conducted at 80 °C.
Quantification: Products were analyzed using gas chromatography with an FFAP capillary column.
The experiments established a clear set of controls: Under continuous-flow conditions with a high ratio of aromatic substrates to hydrogen, the Pt₅Au₅ catalyst maintained stable operation for nearly 40 hours. In contrast, under hydrogen-rich conditions with scarce aromatic substrates, hydrogen-induced migration of Pt atoms occurred, leading to a rapid decay in catalytic activity.
This direct comparison extends the simulation conclusion of "substrate anchoring" from the ps timescale to an engineering timescale of tens of hours. This extension is made possible by programmable, reproducible, and long-term stable flow conditions. The authors also clearly defined a boundary: this mechanism provides "substrate protection for pre-existing Pt ensembles" rather than "self-healing." Once hydrogen-induced migration occurs, simply reintroducing high-concentration aromatics cannot restore activity. Reconstructing the active surface Pt ensemble distribution requires air oxidation treatment at 400 °C.
Figure 4 (d–e)｜(d) Snapshots of surface Pt ensemble structures from molecular dynamics simulations; (e) Evolution of the average Pt–Au coordination number with simulation time.
IV. Scale-up Demonstration: A 42-Day Test of Photovoltaic–Electrolysis–Hydrogen Storage Integration
Following the establishment of the reaction mechanism, the team operated an integrated system under realistic energy conditions. This setup involved photovoltaic power generation, hydrogen production via PEM water electrolysis, and the direct feeding of crude hydrogen (containing approximately 4 vol% water, without drying or purification) into the hydrogenation reactor.
The system operated continuously for 42 days, completely converting 36 L of toluene into methylcyclohexane. The total chemical hydrogen storage capacity exceeded 29,340 L, with a hydrogen storage efficiency of approximately 96.2% and a cumulative turnover number (TON) greater than 79,000. These reaction conditions are significantly milder than those used in conventional industrial LOHC hydrogenation, which typically requires pure hydrogen at temperatures above 150 °C and pressures of 3–5 MPa.
The paper also addresses the limitations of this work. It serves as a validation of technical feasibility rather than a commercial-scale amplification. Further optimization is needed regarding the impurity tolerance of crude hydrogen and the loading of noble metals (the Pt/Au inventory for the 18 g catalyst is approximately US$894).
Figure 5｜(a) Schematic diagram of direct green hydrogen storage and utilization; (b) Real-time curves of hydrogen production and consumption, together with daily-statistics TON; (c) Cumulative TON, cumulative hydrogen storage volume and H₂ uptake capacity; (d–g) Photovoltaic panel array, integrated system setup, water electrolyzer and hydrogenation reactor, and product methylcyclohexane.
Conclusion:
In summary, Academician Nanfeng Zheng’s team at Xiamen University employed Pt ensemble engineering to discover the substrate-anchored stabilization mechanism, enabling efficient aromatic hydrogenation under mild conditions. The researchers validated a prototype system for direct hydrogen storage using crude hydrogen from photovoltaic electrolysis, offering fresh perspectives for the chemical application of intermittent green hydrogen.
The study also acknowledges that the cost of noble metals and tolerance to industrial impurities are key challenges for future work. The long-term continuous-flow control experiments in this study were conducted using the Ou Shisheng automatic catalyst evaluation system. This system provided experimental support for understanding the dynamic evolution of catalysts under practical operating conditions. It is anticipated that more catalytic evaluation tools, which closely simulate industrial realities, will advance the technical implementation of green hydrogen chemistry.
