Mechanism driven design of trimer Ni1Sb2 site delivering superior hydrogenation selectivity to ethylene

Investigation of Sn Promoter on Ni/CeO2 Catalysts for Enhanced Acetylene Semihydrogenation to Ethylene

Ethylene, as an important chemical raw material, could be produced through the coal-based acetylene hydrogenation route. Nickel-based catalysts demonstrate significant activity in the semihydrogenation reaction of acetylene, but they encounter challenges related to catalyst deactivation and overhydrogenation. Herein, the effect of Sn promoter on Ni/CeO2 catalysts has been comprehensively explored for acetylene semihydrogenation. The optimized Ni/8%Sn-CeO2 catalytic performance was significantly improved, with 100% acetylene conversion and 82.5% ethylene selectivity at 250 °C, and the catalyst maintained high catalyst performance within a 1000 min stability test. A series of characterization tests show that CeO2 modified by moderate Sn4+ doping is more conducive to modulating the charge structure and geometry of the Ni active center. Additionally, the in situ Diffuse Reflectance Infrared Fourier Transform Spectroscopy and density functional theory results indicated that catalysts doped with Sn4+ facilitated more efficient desorption of ethylene from the catalyst surface compared to Ni/CeO2 catalysts, thus improving ethylene selectivity and yield. This study highlights an effective strategy for improving the catalytic performance of rare-earth-based catalysts through the incorporation of effective metal promoters.

Thermal Effect Management via Entropy Variation Strategy to Improve the Catalyst Stability in Acetylene Hydrogenation

The dynamic structure evolution of heterogeneous catalysts during reaction has gained great attention recently. However, controllably manipulating dynamic process and then feeding back catalyst design to extend the lifetime remains challenging. Herein, we proposed an entropy variation strategy to develop a dynamic CuZn-Co/HEOs catalyst, in which the non-active Co nano-islands play a crucial role in controlling thermal effect via timely capturing and utilizing reaction heat generated on the adjacent active CuZn alloys, thus solving the deactivation problem of Cu-based catalysts. Specifically, heat sensitive Co nano-islands experienced an entropy increasing process of slowly redispersion during the reaction. Under such heat dissipation effect, the CuZn-Co/HEOs catalyst exhibited 95.7 % ethylene selectivity and amazing long-term stability (>530 h) in the typical exothermic acetylene hydrogenation. Aiming at cultivating it as a catalyst with promising industrial potential, we proposed a simple regeneration approach via an entropy decreasing process.

Ambient-condition acetylene hydrogenation to ethylene over WS2-confined atomic Pd sites

Ambient-condition acetylene hydrogenation to ethylene (AC-AHE) is a promising process for ethylene production with minimal additional energy input, yet remains a great challenge due to the difficulty in the coactivation of acetylene and H2 at room temperature. Herein, we report a highly efficient AC-AHE process over robust sulfur-confined atomic Pd species on tungsten sulfide surface. The catalyst exhibits over 99% acetylene conversion with a high ethylene selectivity of 70% at 25 oC, and a record space-time yield of ethylene of 1123 molC2H4 molPd-1 h-1 under ambient conditions, which is nearly four times that of the typical Pd1Ag3/Al2O3 catalyst, and exhibiting superior stability of over 500 h. We demonstrate that the confinement of Pd-S coordination induces positively-charged atomic Pdδ+, which not only facilitates C2H2 hydrogenation but also promotes C2H4 desorption, thereby enabling a high conversion of C2H2 to C2H4 at room temperature while suppressing over-hydrogenation to C2H6.

Microenvironment Engineering of Heterogeneous Catalysts for Liquid-Phase Environmental Catalysis

Environmental catalysis has emerged as a scientific frontier in mitigating water pollution and advancing circular chemistry and reaction microenvironment significantly influences the catalytic performance and efficiency. This review delves into microenvironment engineering within liquid-phase environmental catalysis, categorizing microenvironments into four scales: atom/molecule-level modulation, nano/microscale-confined structures, interface and surface regulation, and external field effects. Each category is analyzed for its unique characteristics and merits, emphasizing its potential to significantly enhance catalytic efficiency and selectivity. Following this overview, we introduced recent advancements in advanced material and system design to promote liquid-phase environmental catalysis (e.g., water purification, transformation to value-added products, and green synthesis), leveraging state-of-the-art microenvironment engineering technologies. These discussions showcase microenvironment engineering was applied in different reactions to fine-tune catalytic regimes and improve the efficiency from both thermodynamics and kinetics perspectives. Lastly, we discussed the challenges and future directions in microenvironment engineering. This review underscores the potential of microenvironment engineering in intelligent materials and system design to drive the development of more effective and sustainable catalytic solutions to environmental decontamination.

Embedding Single Pd Atoms on NiGa Intermetallic Surfaces for Efficient and Selective Alkyne Hydrogenation

Catalytic removal of alkynes is essential in industry for producing polymer-grade alkenes from steam cracking processes. Non-noble Ni-based catalysts hold promise as effective alternatives to industrial Pd-based catalysts but suffer from low activity. Here we report embedding of single-atom Pd onto the NiGa intermetallic surface with replacing Ga atoms via a well-defined synthesis strategy to design Pd1-NiGa catalyst for alkyne semi-hydrogenation. The fabricated Pd1Ni2Ga1 ensemble sites deliver remarkably higher specific mass activity under superb alkene selectivity of >96 % than the state-of-the-art catalysts under industry-relevant conditions. Integrated experimental and computational studies reveal that the single-atom Pd synergizes with the neighbouring Ni sites to facilitate the σ-adsorption of alkyne and dissociation of hydrogen while suppress the alkene adsorption. Such synergistic effects confer the single-atom Pd on the NiGa intermetallic with a Midas touch for alkyne semi-hydrogenation, providing an effective strategy for stimulating low active Ni-based catalysts for other selective hydrogenations in industry.

Lattice-Strain Engineering in Ni-Ru Heterostructures for Efficient Acetylene Hydrochlorination toward Vinyl Chloride

Ru-based catalysts have emerged as promising alternatives to HgCl2 in vinyl chloride monomer (VCM) production by acetylene hydrochlorination. However, poor C2H2 activation and the generation of key intermediates (*CH2═CH) have posed grand challenges for enhanced catalytic performances. Herein, we synthesized a Ni-intercalated Ru heterostructure using a lattice-strain engineering strategy, resulting in the desired electronic and chemical environments. The collaboration of Ni splits the adsorption centers of C2H2 and HCl by weakening the strong steric hindrance, and it also promotes the activation of the linear C≡C configurations. The well-controlled lattice strain enables strong d-d hybridization interactions between Ni and Ru, resulting in an upshift of the d-band center from -3.72 eV (for Ru/C) to -3.49 eV and electronic delocalization. This optimized local Ni-Ru/C structure thus enhances *H adsorption while weakening the energy barrier for generating *CH2═CH intermediates. Furthermore, the energy barrier for VCM formation was simultaneously reduced. Accordingly, the Ni-Ru/C heterostructures achieve improved performance in pilot-scale trials, with a conversion of >99.2% and stability for over 500 h. These performances significantly surpass most reported Ru-based moieties and the traditional Hg catalysts, offering a promising avenue for C2H2 activation in industrial applications.

Atomic Design of Alkyne Semihydrogenation Catalysts via Active Learning

Alkyne hydrogenation on palladium-based catalysts modified with silver is currently used in industry to eliminate trace amounts of alkynes in alkenes produced from steam cracking and alkane dehydrogenation processes. Intensive efforts have been devoted to designing an alternative catalyst for improvement, especially in terms of selectivity and catalyst cost, which is still far away from that as expected. Here, we describe an atomic design of a high-performance Ni-based intermetallic catalyst aided by active machine learning combined with density functional theory calculations. The engineered NiIn catalyst exhibits >97% selectivity to ethylene and propylene at the full conversion of acetylene and propyne at mild temperature, outperforming the reported Ni-based catalysts and even noble Pd-based ones. Detailed mechanistic studies using theoretical calculations and advanced characterizations elucidate that the atomic-level defined coordination environment of Ni sites and well-designed hybridization of Ni 3d with In 5p orbital determine the semihydrogenation pathway.

Thermally induced intermetallic Rh1Zn1 nanoparticles with high phase-purity for highly selective hydrogenation of acetylene

Ordered M1Zn1 intermetallic phases with structurally isolated atom sites offer unique electronic and geometric structures for catalytic applications, but lack reliable industrial synthesis methods that avoid forming a disordered alloy with ill-defined composition. We developed a facile strategy for preparing well-defined M1Zn1 intermetallic nanoparticle (i-NP) catalysts from physical mixtures of monometallic M/SiO2 (M = Rh, Pd, Pt) and ZnO. The Rh1Zn1 i-NPs with structurally isolated Rh atom sites had a high intrinsic selectivity to ethylene (91%) with extremely low C4 and oligomer formation, outperforming the reported intermetallic and alloy catalysts in acetylene semihydrogenation. Further studies revealed that the M1Zn1 phases were formed in situ in a reducing atmosphere at 400 °C by a Zn atom emitting-trapping-ordering (Zn-ETO) mechanism, which ensures the high phase-purity of i-NPs. This study provides a scalable and practical solution for further exploration of Zn-based intermetallic phases and a new strategy for designing Zn-containing catalysts.

Metal-Organic Framework-Derived Ni-S/C Catalysts for Selective Alkyne Hydrogenation

A carbon matrix-supported Ni catalyst with surface/subsurface S species is prepared using a sacrificial metal-organic framework synthesis strategy. The resulting highly dispersed Ni-S/C catalyst contains surface discontinuous and electron-deficient Niδ+ sites modified by p-block S elements. This catalyst proved to be extremely active and selective for alkyne hydrogenation. Specifically, high intrinsic activity (TOF = 0.0351 s-1) and superior selectivity (>90%) at complete conversion were achieved, whereas an analogous S-free sample prepared by the same synthetic route performed poorly. That is, the incorporation of S in Ni particles and the carbon matrix exerts a remarkable positive effect on catalytic behavior for alkyne hydrogenation, breaking the activity-selectivity trade-off. Through comprehensive experimental studies, enhanced performance of Ni-S/C was ascribed to the presence of discontinuous Ni ensembles, which promote desorption of weakly π-bonded ethylene and an optimized electronic structure modified via obvious p-d orbital hybridization.

Effects of Different Reductive Agents on Zn-Promoted Iron Oxide Phases in the CO2–Fischer–Tropsch to Linear α-Olefins

The pretreatment atmosphere has a significant impact on the performance of iron-based catalysts in carbon dioxide (CO2) hydrogenation. In this study, we investigated the effects of carbon monoxide (CO), syngas (H2/CO), and hydrogen (H2) on the performance of iron-based catalysts during the pretreatment process. To evaluate the structural changes in catalysts after activation and reaction, we analyzed their morphology and particle size, the surface and bulk phase composition, carbon deposition, the desorption of linear α-olefins and reaction intermediates using transmission electron microscope (TEM), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), Mössbauer spectroscopy (MES), temperature-programmed desorption (TPD), and in situ diffuse reflectance infrared Fourier transform spectroscopy (in situ DRIFTS). Raman and XPS showed that the H2 pretreatment catalyst caused the absence of iron carbides due to the lack of carbon source, and the CO and syngas pretreatment catalysts promoted the formation of carbon deposits and iron carbides. While the bulk phase of the CO and syngas pretreatment catalyst mainly consists of iron carbide (FeCx), XRD and MES revealed that the bulk phase of the H2 pretreatment catalyst primarily consisted of metallic iron (Fe) and iron oxide (FeOx). The composition of the phase is closely associated with its performance at the initial stage of the reaction. The formation of olefins and C5+ products is more encouraged by CO pretreatment catalysts than by H2 and syngas pretreatment catalysts, according to in situ DRIFTS evidence. Ethylene (C2H4)/propylene (C3H6)-TPD indicates that the CO pretreatment catalyst is more favorable for the desorption of olefins which improves the olefins selectivity. Based on the analysis of the TEM images, H2 pretreatment stimulated particle agglomeration and sintering. In conclusion, the results show that the CO-pretreatment catalyst has higher activity due to the inclusion of more FeOX and Fe3C. In particular, the presence of Fe3C was found to be more favorable for the formation of olefins and C5+ hydrocarbons. Furthermore, carbon deposition was relatively mild and more conducive to maintaining the balance of FeOx/FeCx on the catalyst surface.