Liquid Metal as Bioinspired and Unusual Modulator in Bioorthogonal Catalysis for Tumor Inhibition Therapy

Bioorthogonal catalysis mediated by Pd-based transition metal catalysts has sparked increasing interest in combating diseases. However, the catalytic and therapeutic efficiency of current Pd⁰ catalysts is unsatisfactory. Herein, inspired by the concept that ligands around metal sites could enable enzymes to catalyze astonishing reactions by changing their electronic environment, a LM-Pd catalyst with liquid metal (LM) as an unusual modulator has been designed to realize efficient bioorthogonal catalysis for tumor inhibition. The LM matrix can serve as a “ligand” to afford an electron-rich environment to stabilize the active Pd⁰ and promote nucleophilic turnover of the π-allylpalladium species to accelerate the uncaging process. Besides, the photothermal properties of LM can lead to the enhanced removal of tumor cells by photo-enhanced catalysis and photothermal effect. We believe that our work will broaden the application of LM and motivate the design of bioinspired bioorthogonal catalysts.     

Catalytically Active and Spectator Ce3+ in Ceria‐Supported Metal Catalysts

Identification of active species and the rate‐determining reaction steps are crucial for optimizing the performance of oxygen‐storage materials, which play an important role in catalysts lowering automotive emissions, as electrode materials for fuel cells, and as antioxidants in biomedicine. We demonstrated that active Ce³⁺ species in a ceria‐supported platinum catalyst during CO oxidation are short‐lived and therefore cannot be observed under steady‐state conditions. Using time‐resolved resonant X‐ray emission spectroscopy, we quantitatively correlated the initial rate of Ce³⁺ formation under transient conditions to the overall rate of CO oxidation under steady‐state conditions and showed that ceria reduction is a kinetically relevant step in CO oxidation, whereas a fraction of Ce³⁺ was present as spectators. This approach can be applied to various catalytic processes involving oxygen‐storage materials and reducible oxides to distinguish between redox and nonredox catalytic mechanisms.     

Reactive Ionic Liquid Enables the Construction of 3D Rh Particles with Nanowire Subunits for Electrocatalytic Nitrogen Reduction

Until now, the synthesis of Rh particles with unusual three‐dimensional (3D) nanostructures is still challenging. A 3D nanostructure enables fast ion/molecule transport and possesses plenty of exposed active surface, and therefore it is of great interest to construct 3D Rh particles catalysts for the N₂ reduction reaction (NRR). Herein, we proposed a reactive ionic liquid strategy for fabricating unusual 3D Rh particles with nanowires as the subunits. The ionic liquid n‐octylammonium formate simultaneously worked as reaction medium, reductant and template for the successful construction of 3D Rh particles. The as‐prepared 3D Rh particles demonstrated excellent activity for electrocatalytic N₂ fixation in 0.1 M KOH electrolyte under ambient conditions with a high NH₃ yield of 35.58 μg h^?1 mg_cat.^?1 at ?0.2 V versus reversible hydrogen electrode (RHE), surpassing most of the state‐of‐the‐art noble metal catalysts. Our reactive ionic liquid strategy thus holds great promise for the rational construction of high‐performance electrocatalysts toward NRR.     

Ring dehydration mechanisms and kinetics of polyamic acid models in solution and in the solid state

We have synthesized and studied the ring dehydration mechanisms and kinetics of polyamic acid models in solution and in the solid state using ¹³C-NMR (solid and liquid), HPLC, FTIR, and x-ray diffraction. Results obtained in solution show the role of temperature, catalysts, and the basicity of the amine in ring dehydration mechanisms and kinetics, as well as conformation and intramolecular bonds in the amic acid bond in the solid state. © 1993 John Wiley & Sons, Inc.     

Loading Copper Atoms on Graphdiyne for Highly Efficient Hydrogen Production

Graphdiyne, as a magical support, can anchor zero valence metal atoms, providing us with an opportunity to develop emerging catalysts with the maximized active sites and selectivity. Herein we report high-performance atom catalysts (ACs), Cu⁰/GDY, by anchoring Cu atoms on graphdiyne (GDY) for hydrogen evolution reaction (HER). The activity and selectivity of this catalyst are obviously superior to that of commercial 20 wt.% Pt/C, and the turnover frequency of 30.52 s⁻¹ is 18 times larger than 20 wt.% Pt/C. Density functional theory (DFT) calculations demonstrate that the strong p-d coupling induced charge compensation leads to the zero valence state of the atomic-scaled transition metal catalyst. Our results show the strong advantages of graphdiyne-anchored metal atom catalysts in the field of electrochemical catalysis and opens up a new direction in the field of electrocatalysis.     

Platinum-Iron(II) Oxide Sites Directly Responsible for Preferential Carbon Monoxide Oxidation at Ambient Temperature: An Operando X-ray Absorption Spectroscopy Study**

Operando X-ray absorption spectroscopy identified that the concentration of Fe²⁺ species in the working state-of-the-art Pt−FeO_x catalysts quantitatively correlates to their preferential carbon monoxide oxidation steady-state reaction rate at ambient temperature. Deactivation of such catalysts with time on stream originates from irreversible oxidation of active Fe²⁺ sites. The active Fe²⁺ species are presumably Fe⁺²O⁻² clusters in contact with platinum nanoparticles; they coexist with spectator trivalent oxidic iron (Fe³⁺) and metallic iron (Fe⁰) partially alloyed with platinum. The concentration of active sites and, therefore, the catalyst activity strongly depends on the pretreatment conditions. Fe²⁺ is the resting state of the active sites in the preferential carbon monoxide oxidation cycle.     

The Co‐Entrapment of a Homogeneous Catalyst and an Ionic Liquid by a Sol–gel Method: Recyclable Ionogel Hydrogenation Catalysts

Molecular hydrogenation catalysts have been co‐entrapped with the ionic liquid [Bmim]NTf₂ inside a silica matrix by a sol–gel method. These catalytic ionogels have been compared to simple catalyst‐doped glasses, the parent homogeneous catalysts, commercial heterogeneous catalysts, and Rh‐doped mesoporous silica. The most active ionogel has been characterised by transmission electron microscopy, X‐ray photoelectron spectroscopy, and solid state NMR before and after catalysis. The ionogel catalysts were found to be remarkably active, recyclable and resistant to chemical change.     

碱助剂对完全液相-热解法CuZnAl催化合成低碳醇性能的影响

采用完全液相技术结合热解方法制备了固定床用CuZnAl催化剂,研究表明,该方法能保留完全液相技术赋予催化剂的特殊性能,可以发展成为将完全液相技术拓展于固定床催化剂的通用方法.在所制催化剂中引入碱助剂同样可以增加C₂₊醇的选择性,但主要不是异丁醇,与现行常规方法制备的催化剂不同.通过对催化剂进行XRD、H₂-TPR、NH₃-TPD-MS、BET等表征,结果表明,不同碱助剂对催化剂的作用方式和影响程度不同,使得催化剂中Cu物种的存在形式和数量、催化剂表面的酸碱性和量以及孔道结构存在差异,进而对催化剂性能产生影响.     

Tuning the Redox Chemistry of a Cr/SiO2 Phillips Catalyst for Controlling Activity,Induction Period and Polymer Properties

The Cr/SiO₂ Phillips catalyst has taken a central role in ethylene polymerization ever since its discovery in 1953. This catalyst is unique compared to other ethylene polymerization catalysts, since it is active without the addition of a metal-alkyl co-catalyst. However, metal-alkyls can be added for scavenging poisons, enhancing the catalyst activity, reducing the induction period and altering polymer characteristics. Despite extensive research into the working state of the catalyst, still no consensus has been reached. Here, we show that by varying the type of metal-alkyl co-catalyst and its amount, the Cr redox chemistry can be tailored, resulting in distinct catalyst activities, induction periods, and polymer characteristics. We have used in-situ UV-Vis-NIR diffuse reflectance spectroscopy (DRS) for studying the Cr oxidation state during the reduction by tri-ethyl borane (TEB) or tri-ethyl aluminum (TEAl) and during subsequent ethylene polymerization. The results show that TEB primarily acts as a reductant and reduces Cr⁶⁺ with subsequent ethylene polymerization resulting in rapid polyethylene formation. TEAl generated two types of Cr²⁺ sites, inaccessible Cr³⁺ sites and active Cr⁴⁺ sites. Subsequent addition of ethylene also revealed an increased reducibility of residual Cr⁶⁺ sites and resulted in rapid polyethylene formation. Our results demonstrate the possibility of controlling the reduction chemistry by adding the proper amount and type of metal-alkyl for obtaining desired catalyst activities and tailored polyethylene characteristics.     

NMR Crystallography Enhanced by Quantum Chemical Calculations and Liquid State NMR Spectroscopy for the Investigation of Se-NHC Adducts**

N-heterocyclic carbene ligands (NHC) are widely utilized in catalysis and material science. They are characterized by their steric and electronic properties. Steric properties are usually quantified on the basis of their static structure, which can be determined by X-ray diffraction. The electronic properties are estimated in the liquid state; for example, via the ⁷⁷Se liquid state NMR of Se-NHC adducts. We demonstrate that ⁷⁷Se NMR crystallography can contribute to the characterization of the structural and electronic properties of NHC in solid and liquid states. Selected Se-NHC adducts are investigated via ⁷⁷Se solid state NMR and X-ray crystallography, supported by quantum chemical calculations. This investigation reveals a correlation between the molecular structure of adducts and NMR parameters, including not only isotropic chemical shifts but also the other chemical shift tensor components. Afterwards, the liquid state ⁷⁷Se NMR data is presented and interpreted in terms of the quantum chemistry modelling. The discrepancy between the structural and electronic properties, and in particular the π-accepting abilities of adducts in the solid and liquid states is discussed. Finally, the ¹³C isotropic chemical shift from the liquid state NMR and the ¹³C tensor components are also discussed, and compared with their ⁷⁷Se counterparts. ⁷⁷Se NMR crystallography can deliver valuable information about NHC ligands, and together with liquid state ⁷⁷Se NMR can provide an in-depth outlook on the properties of NHC ligands.     

Synergic Effect of Active Sites in Zinc‐Modified ZSM‐5 Zeolites as Revealed by High‐Field Solid‐State NMR Spectroscopy

Understanding the nature of active sites in metal‐supported catalysts is of great importance towards establishing their structure–property relationships. The outstanding catalytic performance of metal‐supported catalysts is frequently ascribed to the synergic effect of different active sites, which is however not well spectroscopically characterized. Herein, we report the direct detection of surface Zn species and ¹H–⁶⁷Zn internuclear interaction between Zn²⁺ ions and Brønsted acid sites on Zn‐modified ZSM‐5 zeolites by high‐field solid‐state NMR spectroscopy. The observed promotion of C?H bond activation of methane is rationalized by the enhanced Brønsted acidity generated by synergic effects arising from the spatial proximity/interaction between Zn²⁺ ions and Brønsted acidic protons. The concentration of synergic active sites is determined by ¹H–⁶⁷Zn double‐resonance solid‐state NMR spectroscopy.     

Ammonia synthesis from dinitrogen and dihydrogen over the catalysts based on supported mononuclear potassium carbonyl ruthenate. Promoting effect of alkyllithium compounds

New catalysts for the ammonia synthesis from dinitrogen and dihydrogen based on supported mononuclear potassium carbonyl ruthenate K₂Ru[(CO)₄] as a precursor of catalytically active particles have been developed. Magnesium oxide and graphite-like active carbon Sibunit were used as supports, while aliphatic organolithium compounds (BuⁿLi and Bu^tLi) were employed as electron promoters in these catalysts. The systems with MgO as a support are the most efficient. The introduction of RLi into these systems allows one to considerably increase the ammonia synthesis rate. When using carbon Sibunit, the promoting effect of organolithium compounds is much weaker but the activity of such catalysts can be essentially increased by the introduction of an additional electron promoter, viz., metallic potassium, into the system. All the catalysts tested are active in the ammonia synthesis at atmospheric pressure and temperatures ??250 °C.     

The nature of active sites in Pt promoted GaZSM-5 catalysts

Summary Activity and selectivity of Pt-promoted GaZSM-5 catalysts in the aromatization of ethane were studied. XRD indicated that high temperature treatment of the Pt promoted GaZSM-5 zeolites results in the formation of bimetallic GaPt clusters located on the inner surface of zeolites. Both experimental results and calculations suggest that the clusters containing Ga and Pt atoms stabilized in cationic positions are characterized by an increased activity and selectivity in the dehydrogenation of ethane.</o:p>     

Propylene polymerization with catalysts containing divalent titanium

The behavior in propylene polymerization of divalent titanium compounds of type [η⁶-areneTiAl₂Cl₈], both as such and supported on activated MgCl₂, has been studied and compared to that of the simple catalyst MgCl₂/TiCl₄. Triethylaluminium was used as cocatalyst. The Ti–arene complexes were active both in the presence and in the absence of hydrogen, in contrast to earlier reports that divalent titanium species are active for ethylene but not for propylene polymerization. ¹³C-NMR analysis of low molecular weight polymer fractions indicated that the hydrogen activation effect observed for the MgCl₂-supported catalysts should be ascribed to reactivation of 2,1-inserted (“dormant”) sites via chain transfer, rather than to (re)generation of active trivalent Ti via oxidative addition of hydrogen to divalent species. Decay in activity during polymerization was observed with both catalysts, indicating that for MgCl₂/TiCl₄ catalysts decay is not necessarily due to overreduction of Ti to the divalent state during polymerization. In ethylene polymerization both catalysts exhibited an acceleration rather than a decay profile. It is suggested that the observed decay in activity during propylene polymerization may be due to the formation of clustered species that are too hindered for propylene but that allow ethylene polymerization. © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35: 2645–2652, 1997     

Elucidation of hydrodesulfurization mechanism on molybdenum‐based catalysts using 35S radioisotope pulse tracer methods

Elucidation of the hydrodesulfurization (HDS) mechanism on molybdenum‐based catalysts using radioisotope tracer methods and reaction kinetics is reviewed. Firstly, to investigate the sulfidation state in Mo/Al₂O₃ and Co–Mo/Al₂O₃ catalysts, presulfiding of these catalysts has been performed using a ³⁵S pulse tracer method. Secondly, HDS of radioactive ³⁵S‐labeled dibenzothiophene was carried out over a series of sulfided molybdena–alumina catalysts and cobalt‐promoted molybdena–alumina catalysts in a pressurized flow reactor to estimate the behavior of sulfur on the working catalysts. Finally, sulfur exchange of a ³⁵S‐labeled catalyst with hydrogen sulfide was performed to estimate the relationship between the amount of labile sulfur and catalytically active sites.     

Oxidation of 1,3-butadiene over Pd/C and Pd-Te/C catalysts in polar media

The oxidation of 1,3-butadiene over the Pd/C and Pd-Te/C heterogeneous catalysts occurs in organic solvents containing water at a temperature of 100°C and an oxygen partial pressure of $P_{\left[ {O_2 } \right]} = 4$ atm. Crotonaldehyde dominates among the three major products of oxidation over the Pd catalyst. The introduction of Te into the catalyst increases the methyl vinyl ketone yield, the furan yield being the lowest in all cases. X-ray photoelectron spectroscopy (XPS) showed that the active catalyst components can be in a partially oxidized state, particularly after storing the catalysts in air. Additional hydrogen treatment results in almost complete reduction of the active components to metals and enhances the catalytic activity. It is supposed that the oxidation of 1,3-butadiene over the Pd-Te catalysts proceeds via the activation of dioxygen over the Pd⁰ sites, with oxidized Pd and Te participating in subsequent chemical transformations.     

Polymer‐supported half‐titanocene catalysts for the syndiospecific polymerization of styrene

Monocyclopendienyltitanium trichloride (CpTiCl₃) was supported on polymer carriers with different hydroxyl contents, and the supported catalysts were used for styrene polymerization. The supported catalysts exhibited high activity even at low Al/Ti ratios and increased the molecular weight of the products, indicating that polymer carriers could stabilize the active sites. The polymers prepared with unsupported and supported catalysts were extracted with boiling n‐butanone and characterized by carbon nuclear magnetic resonance (¹³C NMR) and differential scanning calorimetry. The polymers obtained by supported catalysts had a high fraction of boiling n‐butanone‐insoluble part and high melting temperatures, but ¹³C NMR results showed that syndiotacticity decreased compared with that of polymers prepared with an unsupported catalyst. ESR study on the supported catalysts confirmed that the active sites supported on the carrier dropped into the solution and formed active sites the same as those in the unsupported system when they reacted with methylaluminoxane. ¹³C NMR analysis showed that the polymerization mechanism of the supported active sites was an active‐site controlled mechanism instead of a chain‐end controlled mechanism of the unsupported active sites. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 127–135, 2000     

Accelerating Oxygen‐Reduction Catalysts through Preventing Poisoning with Non‐Reactive Species by Using Hydrophobic Ionic Liquids

Developing cost‐effective electrocatalysts for the oxygen reduction reaction (ORR) is a prerequisite for broad market penetration of low‐temperature fuel cells. A major barrier stems from the poisoning of surface sites by nonreactive oxygenated species and the sluggish ORR kinetics on the Pt catalysts. Herein we report a facile approach to accelerating ORR kinetics by using a hydrophobic ionic liquid (IL), which protects Pt sites from surface oxidation, making the IL‐modified Pt intrinsically more active than its unmodified counterpart. The mass activity of the catalyst is increased by three times to 1.01 A mg^?1_Pt@0.9 V, representing a new record for pure Pt catalysts. The enhanced performance of the IL‐modified catalyst can be stabilized after 30 000 cycles. We anticipate these results will form the basis for an unprecedented perspective in the development of high‐performing electrocatalysts for fuel‐cell applications.     

Temperature Hysteresis in Oxidation of CO on Complex Oxide Catalysts

We have used thermal desorption (TD) with mass spectrometric detection of the desorbed species to study the state of the surface of oxide catalysts for oxidation of CO. Detection of weakly bound forms of water and the species H₃O⁺ and HO ₂ ^⋅ in the thermal desorption spectra correlates with the existence of temperature hysteresis in these samples. The data obtained are explained by the reaction occurring in a highly active state via a heterogeneous-homogeneous mechanism, and also by the effect of local superheating. __________ Translated from Teoreticheskaya i Eksperimental'naya Khimiya, Vol. 41, No. 5, pp. 323–327, September–October, 2005.