铁系催化剂的乙烯聚合研究

对系列铁系烯烃聚合催化剂进行了乙烯聚合行为研究。以己烷为溶剂 ,在 80℃、总压 0 73MPa下 ,考察其取代基效应、氢气调节效应、摩尔比n(Al) /n(Fe)对聚合的影响及乙烯与己烯的共聚合行为 。

Single-atom catalysts based on polarization switching of ferroelectric In_(2)Se_(3) for N_(2) reduction

The polarization switching plays a crucial role in controlling the final products in the catalytic pro-cess.The effect of polarization orientation on nitrogen reduction was investigated by anchoring transition metal atoms to form active centers on ferroelectric material In_(2)Se_(3).During the polariza-tion switching process,the difference in surface electrostatic potential leads to a redistribution of electronic states.This affects the interaction strength between the adsorbed small molecules and the catalyst substrate,thereby altering the reaction barrier.In addition,the surface states must be considered to prevent the adsorption of other small molecules(such as *O,*OH,and *H).Further-more,the V@↓-In_(2)Se_(3) possesses excellent catalytic properties,high electrochemical and thermody-namic stability,which facilitates the catalytic process.Machine learning also helps us further ex-plore the underlying mechanisms.The systematic investigation provides novel insights into the design and application of two-dimensional switchable ferroelectric catalysts for various chemical processes.

Fe-Mn/Al_2O_3 catalysts for low temperature selective catalytic reduction of NO with NH_3

A series of Fe‐Mn/Al2O3 catalysts were prepared and studied for low temperature selective catalytic reduction （SCR） of NO with NH3 in a fixed‐bed reactor. The effects of Fe and Mn on NO conversion and the deactivation of the catalysts were studied. N2 adsorption‐desorption, X‐ray diffraction, transmission electron microscopy, energy dispersive spectroscopy, H2 temperature‐programmed reduction, NH3 temperature‐programmed desorption, X‐ray photoelectron spectroscopy （XPS）, thermal gravimetric analysis and Fourier transform infrared spectroscopy were used to character‐ize the catalysts. The 8Fe‐8Mn/Al2O3 catalyst gave 99%of NO conversion at 150？？ and more than 92.6%NO conversion was obtained in a wide low temperature range of 90–210？？. XPS analysis demonstrated that the Fe3＋was the main iron valence state on the catalyst surface and the addition of Mn increased the accumulation of Fe on the surface. The higher specific surface area, enhanced dispersion of amorphous Fe and Mn, improved reduction properties and surface acidity, lower binding energy, higher Mn4＋/Mn3＋ratio and more adsorbed oxygen species resulted in higher NO conversion for the 8Fe‐8Mn/Al2O3 catalyst. In addition, the SCR activity of the 8Fe‐8Mn/Al2O3 cata‐lyst was only slightly decreased in the presence of H2O and SO2, which indicated that the catalyst had better tolerance to H2O and SO2. The reaction temperature was crucial for the SO2 resistance of catalyst and the decrease of catalytic activity caused by SO2 was mainly due to the sulfate salts formed on the catalyst.

High performance ORR electrocatalysts prepared via one-step pyrolysis of riboflavin

Efficient,cost‐effective electrocatalysts for an oxygen reduction reaction(ORR)are currently required for fuel cells.In the present work,riboflavin was used as a cheap,nontoxic carbon and nitrogen precursor to prepare Fe-N-C catalysts via one‐step pyrolysis in the presence of anhydrous iron chloride.Raman spectroscopy indicated that the catalyst containing nitrogen created a great quantity of defects in the carbon structures,while nitrogen adsorption‐desorption isotherms showed that the catalyst was mesoporous.Transmission electron microscopy demonstrated that the Fe-N-C catalyst was composed of very thin,curved and porous graphene layers together with some Fe2O3nanoparticles,and X‐ray diffraction patterns confirmed that the carbon in the catalyst was highly graphitized.X‐ray photoelectron spectroscopy indicated that the active sites for the ORR were primarily composed of graphitic nitrogen,although Fe sites also played an important role.The ORR activity of the Fe-N-C catalyst reached a maximum of4.16mA cm-2,and its chronoamperometric response was found to decrease by only3%after operating for3h at0.66V(vs RHE)in an O2‐saturated0.1mol L-1KOH solution.In contrast,a commercial40wt%Pt/C catalyst with a loading of0.2mgPt cm-2exhibited an activity of4.46mA cm-2and a40%loss of response.The electrochemical performance of this new Fe-N-C catalyst was therefore comparable to that of the Pt/C catalyst while showing significantly better stability.

Catalytic ativities of single-atom catalysts for CO oxidation: Pt_1/FeO_x vs. Fe_1/FeO_x

An FeOx‐based Pt single‐atom catalyst(SAC),Pt1/FeOx,has stimulated significant recent interest owing to its extraordinary activity toward CO oxidation.The concept of SAC has also been successfully extended to other FeOx supported transition metal systems both experimentally and theoretically.However,the FeOx substrate itself(denoted by Fe1/FeOx following the same nomenclature of Pt1/FeOx)as a typical transition metal oxide possesses a very low catalytic activity toward CO oxidation,although it can be viewed as Fe1/FeOx SAC.Here,to understand the catalytic mechanism of FeOx‐based SACs for CO oxidation,we have performed density functional theory calculations on Pt1/FeOx and Fe1/FeOx for CO oxidation to address the differences between these two SACs in terms of the catalytic mechanism of CO oxidation and the chemical behavior of the catalysts.Our calculation results indicated that the catalytic cycle of Fe1/FeOx is much more difficult to accomplish than that of SAC Pt1/FeOx because of a high activation barrier(1.09eV)for regeneration of the oxygen vacancy formed when the second CO2molecule desorbs from the surface.Moreover,density of states and Bader charge analysis revealed differences in the catalytic performance for CO oxidation by the SACs Fe1/FeOx and Pt1/FeOx.This work provides insights into the fundamental interactions between the single‐atom Pt1and FeOx substrate,and the exceptional catalytic performance of this system for CO oxidation.

Iron-Catalyzed Selective Hydrogenation and Hydroboration/Hydrosilylation of CO_(2)

Carbon dioxide(CO_(2))serves as a sustainable carbon source for building biomass,fossil fuels,and organic chemicals.Converting CO_(2) into value-added chemicals or fuels is an ideal approach to achieve carbon cycling.The reduction and conversion of CO_(2),a pivotal aspect of C1 chemistry,have long been a subject of intense research interest.Previous studies have demonstrated that through transition metal catalysis,hydrogen,boranes,and silanes(E-H,E=H,B or Si)act as effective reducing agents to transform CO_(2) into a range of C1 chemicals,such as formate,formaldehyde,and methanol.Over the past decade,research focus in this field has shifted towards utilizing cost-effective metals as catalysts for selective CO_(2) reduction.A comprehensive review of homogeneous iron-catalyzed CO_(2)reduction using E-H is presented,emphasizing reaction mechanisms and selectivity.

Two-dimensional iron-porphyrin sheet as a promising catalyst for oxygen reduction reaction: a computational study

The development of non-platinum(Pt) oxygen reduction reaction(ORR) catalysts with high activity and low cost is of great importance for large-scale commercialization of fuel cells. By means of density functional theory(DFT) computations, we theoretically identified that two-dimensional(2D) iron-porphyrin(Fe-Pp) sheet, in which the active Fe sites are distributed regularly and separately, is an appealing candidate. The pristine Fe-Pp sheet exhibits considerably high catalytic activity and four-electron selectivity for ORR. Especially, the adsorption of ORR intermediates on Fe-Pp sheet can be significantly weakened by the addition of axial cyanogen(CN) ligand, resulting in pronouncedly enhanced ORR activity. More interestingly, the d band center of CN attached Fe-Pp(Fe-Pp-CN) sheet can be further tuned by applying the external tensile or compressive strain, leading to an enhancement or suppression of ORR catalytic performance. In particular, under a small biaxial tensile strain of 2%, the ORR activity of Fe-Pp-CN sheet is even higher than that of Pt and reaches to the top of activity volcano. Our studies open new ways to design effective non-Pt ORR catalysts for fuel cell technology.

Iron-based composite nanostructure catalysts used to produce COx-free hydrogen from ammonia

Iron-based composite nanostructures with ceria or titania as shell coating on naked iron spheres were successfully synthesized and used to catalyze ammonia decomposition. The structure and texture of fresh and used catalysts were characterized by transmission electron microscopy, X-ray diffraction, in situ X-ray diffraction, temperature-programmed reduction by hydrogen, and N2 adsorption-desorption. For ammonia decomposition, the iron-based composite catalyst coated with cerium and titanium showed excellent catalytic activity compared with naked iron sphere catalyst, with the former yielding nearly 100 % ammonia conversions at 650 ℃ and showing high stability in the catalysis test （for 60 h） at 600 ℃ with a space velocity of 24,000 cm3 gcat h-1. These results showed that adding cerium and titanium played a key role in improving catalytic activity for ammonia decomposition and enabling high thermal stability.