Search

Direct methane conversion (DMC) to oxygenates at low temperature is of great value but remains challenging due to the high energy barrier for C−H bond activation. Here, we report that in situ decoration of Pd1‐ZSM‐5 single atom catalyst (SAC) by CO molecules significantly promoted the DMC reaction, giving the highest turnover frequency of 207 h−1 ever reported at room temperature and ~100 % oxygenates selectivity with H2O2 as oxidant. Combined characterizations and DFT calculations illustrate that the C‐atom of CO prefers to coordinate with Pd1, which donates electrons to the Pd1−O active center (L−Pd1−O, L=CO) generated by H2O2 oxidation. The correspondingly improved electron density over Pd−O pair renders a favorable heterolytic dissociation of C−H bond with low energy barrier of 0.48 eV. Applying CO decoration strategy to M1‐ZSM‐5 (M=Pd, Rh, Ru, Fe) enables improvement of oxygenates productivity by 3.2–11.3 times, highlighting the generalizability of this method in tuning metal‐oxo electronic structure of SACs for efficient DMC process. [ABSTRACT FROM AUTHOR]

The development of a single-atom iron catalyst (Fe©SiO2) for the direct conversion of methane to olefins, aromatics, and hydrogen is a breakthrough in the field of nonoxidative conversion of methane (NCM). However, the optimization of the catalyst remains desirable for industrial applications. Herein, 25 transition metals, including Sc, Ti, V, Cr, Mn, Co, Ni, Cu, Y, Zr, Nb, Mo, Tc, Ru, Rh, Pd, Ag, Hf, Ta, W, Re, Os, Ir, Pt, and Au, are selected to replace the central Fe atom for screening out better single-atom catalysts for the NCM. Using the performance on the activation of methane, such as the adsorption energy of methane, the dissociation energy, and the barrier of methane as the screening descriptors, Mn©SiO2, Fe©SiO2, W©SiO2, and Re©SiO2 are first screened out. The remarkable performance of the four catalysts on methane activation is attributed to the unique geometric structure and the d z 2 orbitals of the central metal crossing over the Fermi level, which can benefit the interaction between methane and the catalysts. By considering the catalytic performance on the whole pathway of methane to ethylene, W©SiO2 is finally selected as the most active catalyst for the NCM, which has the lowest rate-determining barrier of 1.62 eV and the smallest free energy span (1.06 eV) of the overall catalytic cycle. [ABSTRACT FROM AUTHOR]

The one-step conversion of ethanol to 1,3-butadiene has achieved a breakthrough with the development of beta zeolite supported dual metal catalysts. However, the reaction mechanism from ethanol to butadiene is complex and has not yet been fully elucidated, and no catalyst screening effort has been done based on central metal atoms. In this work, density functional theory (DFT) calculations were employed to study the mechanism of one-step conversion of ethanol to butadiene over Zn-Y/BEA catalyst. The results show that ethanol dehydrogenation prefers to proceed on Zn site with a reaction energy of 0.77 eV in the rate-determining step, and the aldol condensation to produce butadiene prefers to proceed on Y site with a reaction energy of 0.69 eV in the rate-determining step. Based on the mechanism revealed, six elements were selected to replace Y for screening superior combination of Zn-M/BEA (M=Sn, Nb, Ta, Hf, Zr, Ti; BEA: beta polymorph A) for this reaction. As a result, Zn-Y/BEA (0.69 eV) is proven to be the most preferring catalyst compared with the other six ones, and Zn-Zr/BEA (0.85 eV), Zn-Ti/BEA (0.87 eV), and Zn-Sn/BEA (0.93 eV) can be potential candidates for the conversion of ethanol to butadiene. This work not only provides mechanistic insights into one-step catalytic conversion of ethanol to butadiene over Zn-Y/BEA catalyst but also offers more promising catalyst candidates for this reaction. [ABSTRACT FROM AUTHOR]

Recently discovered homogeneous frustrated Lewis pairs (FLPs) have attracted much attention for metal-free catalysis due to their promising potential for the activation of small molecules (e.g., H2, CO, CO2, NOx and many others). Hence, a wide range of these homogeneous FLPs have been extensively explored for many advanced organic syntheses, radical chemistry and polymerizations. In particular, these FLPs are efficiently utilized for the hydrogenation of various unsaturated substrates (e.g., olefins, alkynes, esters and ketones). Inspired by the substantial progress in these homogeneous catalytic systems, heterogeneous FLP catalysts, including semi-solid and all-solid catalysts, have also emerged as an exciting and evolving field. In this review, we highlight the recent advances made in heterogeneous FLP-like catalysts and the strategies to construct tailorable interfacial FLP-like active sites on semi-solid and all-solid FLP catalysts. Challenges and outlook for the further development of these catalysts in synthetic chemistry will be discussed. [ABSTRACT FROM AUTHOR]

• Supported bimetallic catalysts typically possess superior performances than monometal catalysts and the impregnation method has been widely applied for the bimetallic catalyst preparations. • Impregnation sequences could play their significant roles on the physical and chemical properties of supported bimetallic catalysts. • A host of characterizations from impregnation sequential effects were briefly evaluated by reviewing the recent representative literatures. • The investigation of the nature of active sites and the structural dynamics on bimetallic catalysts are prospected accordingly to enhance the fundamental understanding of sequential influences. • The appropriate measurement of reaction rates is much required to compare the bimetallic catalysts that are prepared by different sequences of impregnations. Supported bimetallic catalysts have been paid great attention regarding their excellent catalytic performances in chemical process. Notably, comparing to monometallic catalysts, the synergetic properties of dual-metal-based materials demonstrate unique physiochemical functionalities that single metal materials do not possess. The preparation of supported bimetallic materials is widely conducted with applying the impregnation method because of the straightforward and inexpensive technique. Wherein, the impregnation of dual metals on support could either undergo co-impregnation or sequential impregnations. It has been frequently reported that there are substantial differences in physiochemical properties and catalyst performances by impregnation sequences. Specifically, during the investigation of various sequential impregnated bimetallic catalysts, a host of characterization strategies are employed to compare the physical and chemical properties that play vital role to impact the catalyst activity/selectivity/stability. However, it is still not well understood regarding the impregnation sequential effects, such as the nature of bimetallic active sites and the dynamics of bimetallic surface structures along with reaction progress. This presenting perspective article is devoted to take a succinct review regarding the general sequential impacts on the physiochemical properties and further profoundly address the research outlook in this topic. [Display omitted]. [ABSTRACT FROM AUTHOR]

[Display omitted] • Ionic liquid was chemically bonded to mesoporous HAP. • High utilization of hydroxyl binding (90 %) produced high ILs loading (0.468 mmol/g). • High yield (98.7%) and high selectivity (100%) of propylene carbonate (PC). • Autocatalysis was found in the CO 2 fixed reaction. In this study, hydroxyapatite (HAP) with abundant surface hydroxyl and large pores was used as the ionic liquid ([DMCA]X) immobilization carrier, where the surface hydroxyl groups of HAP were used as binding sites and the n-halogen-acids were used as bonding agents. The supported ionic liquid catalysts [DMCA]X-n-HAP were characterized by XRD, TEM, TG and FTIR, proving that the ionic liquids were successfully bonded onto the surface of HAP. The utilization of hydroxyl sites on the surface of HAP was as high as 90%. The above catalysts were used to catalyze the cycloaddition reaction of CO 2 and propylene oxide (PO), and the yield and selectivity of propylene carbonate (PC) were up to 98.7% and 100%, respectively. The length effect of the bonding agents on the catalyst performance was also studied, and found that n-chlorine-butyric acid was the most suitable chemical for channel structure of HAP and spatial freedom of ionic liquid. In addition, the effects of halogen anion and hydroxyl hydrogen on the performance of the reaction were also studied. Importantly, autocatalysis was discovered in the reaction. Finally, the reaction intermediates and reaction mechanism of CO 2 cycloaddition were investigated by in situ -DRIFTS, revealing that ring-open of PO is rate-determining step. [ABSTRACT FROM AUTHOR]

Relevant parameters for the leaching of palladium atoms from small Pd clusters during Heck reactions of bromobenzene and styrene have been explored computationally and experimentally. With density functional theory calculations, we modeled reaction free energies for removing a Pd atom from a Pd 6 model cluster and for forming Pd-ligand complexes. Oxidative addition of bromobenzene decreases the dissolution energy. Additional parameters and mechanisms, especially bromide ions render the leaching process notably exergonic. Model results exhibit the same trends as the targeted experiments where Pd leaching from supported catalysts (Pd/C, Pd/SiO 2) was monitored as function of reaction temperature, time and components. [Display omitted] • Direct correlation of palladium leaching with reaction rate of Heck coupling. • Quantification of Pd dissolution as function of temperature, time and composition. • Aryl halide, alkene and bromide favor leaching singly and in combination. • Qualitative agreement of DFT model simulations with closely targeted experiments. [ABSTRACT FROM AUTHOR]