Search

An egg-shell-type Ag/SiO2 pellet catalyst with an optimized thickness of the Ag-shell exhibits both enhanced activity and selectivity for DMO hydrogenation to MG.

Structure–performance relationship is a complex issue in iron-catalyzed Fischer–Tropsch synthesis, and it is not easy to elucidate it by experimental investigations. First-principle calculation is a powerful method for explaining experimental results and guiding catalyst design. In this study, we investigated the reaction mechanisms of CH4 formation and C–C coupling on four χ-Fe5C2 surfaces and established the kinetic equations to compare the rates of CH4 formation and C1+C1 coupling reactions and determine the CH4/C2+ selectivity. The results show that the geometry of the χ-Fe5C2 surfaces has little effect on the formation rate of CH4; however, the C1+C1 coupling reactions are significantly affected by the surface geometry. The C1+C1 coupling reaction rates on the terraced-like (510) and (021) surfaces are much higher than those on the stepped-like (001) and (100) surfaces. Based on these results, we established a Bronsted–Evans–Polanyi (BEP) relationship between the effective barrier difference for CH4 formation and C1+C1 coupling (ΔEeff) and the adsorption energy of C+4H (ΔEC+4H) on χ-Fe5C2 surfaces. ΔEC+4H can be used as a descriptor for CH4/C2+ selectivity on different surfaces of χ-Fe5C2.

Recycling performance of heterogeneous catalysts is of crucial importance especially for a batch reaction system. In this work, we demonstrate a strategy for enhancing recycling performance of Ir-Re/SiO2 catalyst synergized with amberlyst-15 in glycerol hydrogenolysis to produce 1,3-propanediol. Comprehensive characterization results reveal that the Re sites in the Ir-Re/SiO2 catalyst undergo irreversible segregation and oxidation. These hinder the formation of active Re-OH species and thus contribute to a complete and irreversible deactivation. However, the introduction of amberlyst-15 into the reactant mixture can restrain the oxidation process of Re sites and favor the formation of Re-OH species, and thus significantly enhance the catalytic recycling performance. The results demonstrated here could guide the development of excellent bimetallic catalysts with the desirable recycling performances for the reaction.

A subsurface carbon tailored Ni–Ga intermetallic catalyst delivers superior catalytic performance for acetylene semi-hydrogenation.

The effect of gases on the surface composition of Cu–Pt bimetallic catalysts has been tested by in situ infrared (IR) and x-ray absorption spectroscopies. Diffusion of Pt atoms within the Cu–Pt nanoparticles was observed both in vacuum and under gaseous atmospheres. Vacuum IR spectra of CO adsorbed on CuPtx/SBA-15 catalysts (x = 0–∞) at 125 K showed no bonding on Pt regardless of Pt content, but reversible Pt segregation to the surface was seen with the high-Pt-content (x ≥ 0.2) samples upon heating to 225 K. In situ IR spectra in CO atmospheres also highlighted the reversible segregation of Pt to the surface and its diffusion back into the bulk when cycling the temperature from 295 to 495 K and back, most evidently for diluted single-atom alloy catalysts (x ≤ 0.01). Similar behavior was possibly observed under H2 using small amounts of CO as a probe molecule. In situ x-ray absorption near-edge structure data obtained for CuPt0.2/SBA-15 under both CO and He pointed to the metallic nature of the Pt atoms irrespective of gas or temperature, but analysis of the extended x-ray absorption fine structure identified a change in coordination environment around the Pt atoms, from a (Pt–Cu):(Pt–Pt) coordination number ratio of ∼6:6 at or below 445 K to 8:4 at 495 K. The main conclusion is that Cu–Pt bimetallic catalysts are dynamic, with the composition of their surfaces being dependent on temperature in gaseous environments.

Selective hydrogenation of alkynes in C2 and C3 streams from steam cracking of naphtha is significant for the production of polymer-grade ethylene and propylene. Herein, a comprehensive thermodynam...

Summary Mechanism-guided catalyst design and engineering at the scale of active sites has been developed as a powerful tool for boosting catalytic performance. Herein, we report an efficient selective silylation strategy for the elaborate fabrication of ternary Au–Ti–Si sites to boost propylene epoxidation with H2 and O2. Kinetics (isotopic) analysis, Fourier transform infrared measurements, and theoretical calculations indicate an urgent necessity for selective consuming silanol sites not only to suppress propylene oxide (PO) ring opening to byproducts promoted by H2 spillover but also to minimize PO inhibition effects. A continuous silylation treatment was developed to encourage the kinetically favorable formation of ternary Au–Ti(–OH)–Si(–O–SiR3) moiety. This delivers significantly improved H2 efficiency of 42.5% in addition to the promising PO formation rate of 193 g h−1 kgcat−1 and PO selectivity of 95.7% with the long-term stability in excess of 200 h. These insights could pave the way for rationally fabricating catalyst active sites toward optimized performance.

Ag catalysts are promising for the selective hydrogenation of dimethyl oxalate (DMO) to methyl glycolate (MG), where the size of Ag nanoparticles strongly dominates their catalytic performances. Fundamental understandings on the size dependence, especially at the level of active sites, are still lacking but of great importance for the rational design of Ag-based catalysts for this reaction. Herein, a series of catalysts consisting of Ag nanoparticles sized from 2.9 to 8.8 nm anchored on amine-derivatized mesoporous silica nanospheres (Ag/AS) were synthesized and employed to understand the size-dependent DMO hydrogenation to MG. A volcano-shape trend between the hydrogenation activity and the increasing Ag particle size is observed for the differently sized Ag/AS catalysts, indicating a remarkable size dependence. The origin of the size dependence is further understood based on the cuboctahedron model of Ag nanoparticle, and the step-likes active sites are identified as the dominant ones. Results combining with the X-ray photoelectron spectroscopy, in situ Fourier transform infrared spectroscopy and temperature programmed desorption studies, indicate that the hydrogenation of DMO to MG on Ag/AS catalysts is mainly dominated by the number of active sites when the Ag particle size ≥ 5.3 nm, but by the electronic properties when the Ag particle size

Summary The principle of how the active sites of catalysts match the reaction intermediates has long been sought after. Herein, we report a theory-guided atomic design and fabrication strategy of a C-based catalyst with diatomic Fe–Ni and N,P co-doping for the oxygen evolution reaction (OER). The configuration matching (with O∗ on the Ni site and OH∗ on the adjacent Fe site) and the local electron engineering by P doping significantly facilitate the rate-determining step of OOH∗ formation. Such diatomic Fe–Ni is demonstrated to be thermodynamically stable and is precisely constructed through the pyrolysis of Fe3+/Ni2+-adsorbed ZIF-8 under NaH2PO2 co-feeding. The synergistic effects endow the catalyst with a low overpotential and high turnover frequency, exceeding all transition-metal N-based catalysts so far as we know, which provides a deep understanding of the OER mechanism on heteroatomic metal-based catalysts. This strategy will pave the way for novel catalyst design and the replacement of noble-metal-based catalysts.

Producing lower olefins via iron-based Fischer-Tropsch synthesis without intermediate process has received increasing interests. Herein, effects of support modification on FTO performance of CNT supported Fe catalysts are comparatively investigated. Employing the defect-rich CNT as the catalyst support compared to the pristine CNT support is found to exhibit the shorter induction period and higher iron time yield (FTY). The promotional effects of K and Mn promoters on the FTO performance are subsequently revealed on the defect-rich CNT supported Fe catalysts. Both promoters are observed to suppress the formation of undesirable methane and to enhance the selectivity to desirable lower olefins. Moreover, the introduction of the Mn promoter facilitates the dispersion of iron particles and thus shows higher FTY, and it also gives rise to much higher catalyst stability than the K promoter. The insights reported here could guide the design and optimization of promoted Fe/C FTO catalysts.

Modulating the metal–support interaction is a promising way to tailor the electronic structure of metal nanoparticles and hence alter their catalytic performance. Here, we developed a reduced TiO2 with rich oxygen vacancies on which to load Pd for catalytic oxidation of formaldehyde (HCHO) at room temperature. The reduced TiO2 remarkably induced an electronic metal–support interaction by transferring electrons from the support to Pd to form negatively charged Pd nanoparticles, facilitating the oxygen association. Simultaneously, the reduced TiO2 significantly increased the dispersion and the reduction degree of Pd compared with the pristine TiO2 by offering more anchor sites and electron-rich sites. Furthermore, the abundant oxygen vacancies in the reduced TiO2 show a synergistic effect by enabling the effective adsorption and dissociation of water to generate surface hydroxyl groups, accelerating the kinetics of active oxygen species generation and promoting the complete conversion of 100 ppm HCHO at a WHSV of 120,000 mL/(gcat·h). We tentatively propose two reaction mechanisms for HCHO oxidation over Pd-loaded oxygen-vacancy-rich TiO2 involving active oxygen species.

Fundamental understanding of the size effects of Pt-electrocatalyzed methanol oxidation reaction (MOR) in the alkaline media is rarely explored, especially from the viewpoint of catalyst active sites. Herein, we report a remarkable size-dependent MOR activity of atomic-layer-deposited Pt nanoparticles on CNT. The surface properties of CNT are tailored, and using the growth temperature of 600 °C followed by the oxidation treatment is found to yield an attractive support, i.e., CNT-600-O, for the fabrication of highly active Pt catalysts. On such support, the 1.9 nm sized Pt catalyst gives rise to the highest peak current density, which is approximately 3.2 times higher than the commercial Pt/C catalyst. The underlying nature of the Pt size effects is further elucidated by the model calculations together with HRTEM and XPS measurements. The Pt corner sites are discriminated as the dominant active sites, and the lower Pt° 4f binding energy favors the reaction. The insights revealed here could shed light on the fabrication of highly efficient Pt-based MOR catalyst by tailoring the quantity and quality of the catalyst active sites.

In this study, the support effects on the Pd-catalyzed semi-hydrogenation of acetylene have been investigated from the structural and kinetic perspectives. According to the results of kinetic analysis and X-ray photoelectron spectroscopy, hydrogen temperature-programmed reduction, temperature-programmed hydride decomposition, and in situ X-ray diffraction measurements, using carbon nanotubes as support for Pd nanocatalysts with various sizes instead of α-Al2O3 decreases the Pd0 3d binding energy and suppresses the formation of undesirable palladium hydride species, thus increasing the ethylene yield. Furthermore, X-ray absorption spectroscopy, high-resolution transmission electron microscopy, and C2H4 temperature-programmed desorption studies combined with density-functional theory calculations reveal the existence of a unique Pd local environment, containing subsurface carbon atoms, that produces positive geometric effects on the acetylene conversion reaction. Therefore, tailoring the Pd local environment and electronic properties represents an effective strategy for the fabrication and design of highly active and selective Pd semi-hydrogenation catalysts.

Exploration of cost-effective Pt/C catalysts has been a significant issue for electrochemical hydrogen evolution reaction (HER) toward sustainable energy conversion and storage. Herein, we report a fabrication strategy by employing platelet carbon nanofibers (p-CNF) as the support to immobilize Pt-CoO HER electrocatalyst using atomic layer deposition method. The edge-rich p-CNF support is found to act as the anchoring sites of Pt nanoparticles and favorably capture electrons from Pt to yield electron-deficient Pt surfaces for the boosted HER. Additionally, the sequential growth of CoO onto the Pt/p-CNF catalyst elaborately constructs the Pt-CoO interface and facilitates the electron transfer from Pt to CoO, which further enhances the HER activity. These advantages endow the fabricated Pt-CoO/p-CNF catalyst with the superior HER activity, e.g., a very low overpotential of 26 mV at the current density of 10 mA·cm−2 and a mass activity of 4.42 A·mgPt−1 at the overpotential of 30 mV, 18.8 times higher than that of the commercial 20 wt% Pt/C catalyst. The insights reported here could shed light on for the fabrication of cost-effective Pt-based composite HER catalysts.

The kinetics of dimethyl oxalate (DMO) hydrogenation over Cu(111) and Cu2O(111) has been studied to understand the role of Cu0 and Cu+ sites in ethyl glycol (EG) production over Cu-based catalysts ...

The development of high-performance glucose sensors is an urgent need, especially for diabetes mellitus diagnosis. However, the glucose monitoring is conventionally operated in an invasive finger-prick manner and their noninvasive alternatives largely suffered from the relatively poor sensitivity, selectivity, and stability, resulted from the lack of robust and efficient catalysts. In this paper, we design a concave shaped nitrogen-doped carbon framework embellished with single Co site catalyst (Co SSC) by selectively controlling the etching rate on different facet of carbon substrate, which is beneficial to the diffusion and contact of analyte. The Co SSC prompts a significant improvement in the sensitivity of the solution-gated graphene transistor (SGGT) devices, with three orders of magnitude better than those of SGGT devices without catalysts. Our findings expand the field of single site catalyst in the application of biosensors, diabetes diagnostics and personalized health-care monitoring.

Herein, we report the crucial importance of C-defective sites on the CO adsorption over ϵ-Fe2 C and η-Fe2 C Fischer-Tropsch catalysts via systematic DFT calculations. The simulated XRD and Wulff construction show the significant differences in their equilibrium shapes and most exposed surfaces. It is observed that the ϵ-Fe2 C exposes a high proportion (89 %) of facets (1 2 ‾ 1) with similar structure to that of η-Fe2 C (011) which has been proved to be the active surface of CO activation.

Developing efficient catalysts for the selective hydrogenation of dimethyl oxalate (DMO) is of great significance for the coal-based production of methyl glycolate (MG), but designing processes for this conversion is challenging. Herein we report an unprecedented catalytic performance for the selective hydrogenation of DMO to MG, achieved by using a catalyst based on Ag nanoparticles anchored inside the mesopores of amine-derivatized silica nanospheres (NH2-MSNS). It was determined that the unique microenvironment endowed by the amine-derivatized channel surfaces helps this Ag catalyst promote the activation of DMO and H2 to yield MG with high selectivity, and also prevents sintering and coking, hence improving stability. Accordingly, the resulting Ag/NH2-MSNS catalyst was shown to be capable of promoting the hydrogenation reaction with a turnover frequency of 230 h−1 and a MG selectivity of 97% at nearly 100% of DMO conversion, a performance that was sustained for at least 250 h; these results are significantly better than those seen with other reported catalysts. Our study points to a promising route for the development of high-performing Ag catalysts to be used in the coal-based MG production.

Heteroatom-doping of carbocatalysts has been a powerful strategy to remarkably enhance the catalytic performance. Herein, the underlying nature of N promotional effects on peroxymonosulfate (PMS) activation for phenol removal is understood by combining kinetics analysis with multiple techniques. A strategy using mixed acid oxidation of carbon nanotube (CNT) followed by NH3 treatment is employed to yield a series of catalysts with different N-doping contents but similar fraction of sp2-hybridized carbon and defective degree, endowing with a chance to discriminate the dominant N-containing active sites. The multi-sites kinetics analysis suggests the graphitic N-containing sites as the dominant active sites. The mechanism of the surface-bound reactive species is also discriminated as the dominant reaction mechanism. The insights reported here could provide the methodology to fundamentally understand the heteroatom-doping effects of carbocatalysis.

The particulate matter of size less than 2.5 μm (PM2.5) in haze not only affects human health but also reduces the efficiency of fuel cells. Herein, we report for the first time the underlying natu...

Atomic regulation of metal catalysts has emerged as an intriguing yet challenging strategy to boost product selectivity. Here, we report a density functional theory-guided atomic design strategy for the fabrication of a NiGa intermetallic catalyst with completely isolated Ni sites to optimize acetylene semi-hydrogenation processes. Such Ni sites show not only preferential acetylene π-adsorption, but also enhanced ethylene desorption. The characteristics of the Ni sites are confirmed by multiple characterization techniques, including aberration-corrected high-resolution scanning transmission electron microscopy and X-ray absorption spectrometry measurements. The superior performance is also confirmed experimentally against a Ni5 Ga3 intermetallic catalyst with partially isolated Ni sites and against a Ni catalyst with multi-atomic ensemble Ni sites. Accordingly, the NiGa intermetallic catalyst with the completely isolated Ni sites shows significantly enhanced selectivity to ethylene and suppressed coke formation.

A comprehensive study of the kinetics of the catalytic hydrogenation of unsaturated aldehydes, in particular of cinnamaldehyde, promoted by CuPtx/SBA-15 single-atom alloy catalysts was carried out ...

Glycerol hydrogenolysis to 1,3-propanediol is identified to follow the dehydration-hydrogenation pathway with the rate-determining step (RDS) of H* + OH* → H

A molecular-level understanding of how the electronic structure of metal center tunes the catalytic behaviors remains a grand challenge in heterogeneous catalysis. Herein, we report an unconventional kinetics strategy for bridging the microscopic metal electronic structure and the macroscopic steady-state rate for CO oxidation over Pt catalysts. X-ray absorption and photoelectron spectroscopy as well as electron paramagnetic resonance investigations unambiguously reveal the tunable Pt electronic structures with well-designed carbon support surface chemistry. Diminishing the electron density of Pt consolidates the CO-assisted O2 dissociation pathway via the O*-O-C*-O intermediate directly observed by isotopic labeling studies and rationalized by density-functional theory calculations. A combined steady-state isotopic transient kinetic and in situ electronic analyses identifies Pt charge as the kinetics indicators by being closely related to the frequency factor, site coverage, and activation energy. Further incorporation of catalyst structural parameters yields a novel model for quantifying the electronic effects and predicting the catalytic performance. These could serve as a benchmark of catalyst design by a comprehensive kinetics study at the molecular level., A molecular-level understanding of the electronic effects remains a grand challenge in heterogeneous catalysis. Here, the authors report an unconventional kinetics strategy for bridging the upscaling gap between the microscopic fingerprints of active sites and the macroscopic catalytic performance.