Journal of Catalysis最新文献

Catalyst interface determines the activity and stability of partial oxidation of methane (POM) toward syngas under high temperatures crucially. Herein, Ni catalysts supported on CeO₂ were prepared under different pretreatment atmospheres to construct an optimal and robust interface. Ni/CeO₂ catalyst pretreated in H₂ (Ni/CeO₂-H₂) exhibits the higher activity and the better stability than Ni/CeO₂-Ar and Ni/CeO₂-air catalysts. The Ni-O-Ce interfacial site in Ni/CeO₂-H₂ catalyst shows the lower reduction temperature, indicating the enhanced H-spillover effect and enhanced oxidation resistance of Ni under POM conditions. Moreover, the XPS and in situ Raman results show that Ni/CeO₂-H₂ contains more surface oxygen vacancies for adsorbing and activating oxygen, further contributing to the reaction activity. The in situ DRIFTS results indicate that the CH₄ could react with the lattice oxygen to form formate and carbonate, and further decompose to CO and CO₂. These findings deepen the fundamental understanding of Ni/CeO₂ catalysts for POM reaction.

Cu-based Fenton-like systems have demonstrated high effectiveness in the degradation of organic pollutants, however, challenges still exist to overcome the sluggish cycling of metal ions and fast activation of reactants. Herein, a novel n-p type Cu₂(OH)₃F/Cu₂O photo-Fenton-like catalyst (CFC) was prepared with in-situ reduction of Cu₂(OH)₃F and applied for tetracycline hydrochloride degradation. Under optimized condition, the target catalyst (CFC-5) showed excellent activity, achieving a degradation efficiency of approximately 99.93 % in 30 min. The reaction rate constant with CFC-5 was 4.10 and 3.26 times higher than that of Cu₂(OH)₃F and Cu₂O, respectively. Moreover, the Cu₂(OH)₃F/Cu₂O catalyst exhibited highly cycling stability and broad applicability. The results illustrate that construction of Cu₂(OH)₃F/Cu₂O composites facilitates the charge separation and enhances Cu²⁺/Cu⁺ cycling, which benefits the generation of highly oxidizing active species and thus significantly improved the degradation efficiency. Besides, this study offers a versatile method to construct inexpensive and efficient photo-Fenton-like heterojunction catalysts.

The mono-metal relay catalysis is a good strategy for one-pot multi-step cascade process in which the specific catalysis can be switched upon the ligand exchange to match the requirements for each independent reaction but without mutual interference and quenching problem. Herein, the one-pot cascade bis-alkoxycarbonylation of terminal alkynes was achieved by taking advantages of the mono-metallic (Pd) relay catalysis, wherein the two kinds of divergent di-phosphines of L1 and DTBPMB were involved. In this Pd(OAc)₂-L1-DTBPMB system, due to the steric bulkiness of L1 and DTBPMB, the two type of catalysts including Pd(OAc)₂-L1 and Pd(OAc)₂-DTBPMB co-existed independently and compatibly. Pd(OAc)₂-L1 system was only in charge of the first-step carbonylation of alkynes towards the branched α,β-unsaturated esters with gem-positioned double bond. Subsequent, Pd(OAc)₂-DTBPMB system took over the carbonylation of the branched α,β-unsaturated esters to afford the target diesters. It was indicated Pd(OAc)₂-L1 system was an efficient and stable catalyst which could be recycled upon 15 runs for the first-step carbonylation. Anyway, Pd(OAc)₂-DTBPMB system easily underwent deactivation, which degraded the recyclability of the Pd(OAc)₂-L1-DTBPMB coupling system for this cascade bis-alkoxycarbonylation.

Intermetallic compounds (IMCs) are promising catalysts for upgrading biomass-derived platform chemicals. Herein, bifunctional NiSi IMCs catalysts were developed for the hydrogenation and oxidation of cinnamaldehyde (CAL). A solvent-free arc-melting method was employed for the synthesis of NiSi IMCs within 5 min. The NiSi IMCs catalysts afforded 99 % conversion of CAL and presented ∼ 71 % yield of 2-phenyl propanol and ∼ 34 % yield of benzaldehyde for the hydrogenation and base-free oxidation of CAL, respectively. Moreover, NiSi IMCs could be used for five runs without deactivation. Characterizations and theoretical calculation results indicated the formation of intermetallic structure and the existence of Si vacancy sites, which could not only facilitate the efficient hydrogenation of CAL but also expose NiO_x species as catalytic centers for the oxidation of CAL, leading to the high performance and stability in both hydrogenation and oxidation process.

In heterogeneous catalysis, ionic liquids (ILs) are used as chemical modifiers to control selectivity. In our work, we aim to apply the same concept to electrocatalytic systems. As a model reaction, we studied the electrooxidation of 2,3-butanediol on the low-index Pt(1 1 1), Pt(1 0 0) and Pt(1 1 0) surfaces in an acidic environment. We used the IL 1-ethyl-3-methylimidazolium trifluoromethanesulfonate ([C₂C₁Im][OTf]) dissolved in an aqueous electrolyte as a catalyst modifier. The reaction mechanisms were investigated by electrochemical infrared reflection absorption spectroscopy (EC-IRRAS). The oxidation of 2,3-butanediol is highly structure dependent. On all three surfaces, the two products formed are acetoin and diacetyl, i.e. either one or two alcohol functionalities are oxidized. However, we observe distinct features on the different surfaces with respect to activity, potential window of oxidation, and selectivity. Only the Pt(1 0 0) surface is active towards CC bond cleavage. The latter reaction leads to the formation of CO_ads and poisoning of the catalyst. Modification of this surface by addition of the IL leads to an increase of the selectivity for acetoin from 51 % to 78 % (at 1.1 V_RHE). In addition, CC bond cleavage is suppressed, no CO is formed, and the surface remains active for the target reaction. We attribute these effects to the reversible and structure dependent adsorption of the [OTf]⁻ anions on the Pt surfaces and additional interionic interactions. Our results demonstrate the potential of ILs to control selectivity in electrocatalytic reactions.

Photocatalytic hydrogen evolution reaction (photoHER) is one of the most promising approaches towards production of “green” hydrogen. Currently, the state-of-the-art photoHER systems require the use of sacrificial electron donors (SED), because of inefficient charge separation in photosensitizers and thermodynamically challenging water oxidation by the same catalyst. Here, we present a molecular design approach for all-organic photosensitizers with effective intramolecular charge separation, microsecond lifetime of excited states, controllable direction of electron transfer, and ability to oxidize water for recovery of the photocatalytic system to its initial state. Such photosensitizers comprise weakly conjugated strong electron donor and acceptor what enables charge transfer during the light absorption. The excitation energy is stored in long-living triplet states, whose lifetime can be monitored by the thermally activated delayed fluorescence. Additionally, application of heavy-atom effect helps not only to increase the population of triplet state but also to increase its stability and lifetime. When such photosensitizers are attached to the platinized TiO₂, efficient photoHER catalysts are obtained which produce H₂ under irradiation with sunlight. In the presence of SED, the highest turnover number after 24 h (TON_24h) of such systems exceed 3500, whilst in pure water without any SED, TON_24h reaches 2000. Our best system performs photocatalytic SED-free water-splitting for 48 h keeping 100 % of its activity and constant turnover frequency of 26 h⁻¹. The described here investigations reveal that water splitting can be performed by a simple three component system “photosensitizer|TiO₂|Pt” under specific control of 1) the charge separation and its direction, 2) intersystem crossing rate and triplet state lifetime, and 3) favorable water oxidation thermodynamics within a photosensitizer together with 4) appropriate alignment of energy levels to the catalyst.

Insufficient photocatalytic NO_x oxidation capacity will lead to excessive toxic by-products (NO₂), which still seriously restrict its practical application. Herein, the multiple active sites (Cl, Bi⁰ and OVs) modified Bi₂WO₆ has been established by in-situ synthesis method. The synergistic effect of multiple active sites greatly increased the photo-electric properties of the Bi₂WO₆, resulting in the boosting photocatalytic NO_x deep oxidation to nitrate. The visible light driven OVs-Bi@BWO-Cl catalyst exhibited a highest NO conversion efficiency (67.3 %) with extremely low NO₂ concentration (17.9 ppb). The synergism of structural regulation from the OVs with Cl-doping and surface plasmon resonance of Bi⁰ significantly enhanced light absorption and provided a fast charge transport channel, improving the separation efficiency of photo-generated carriers. The in-situ DRIFTS and density functional theory (DFT) results shown that the synergistic effect by multiple active sites could enhance the adsorption and activation of reactants to accelerate the processes of H₂O/O₂-to-ROS and decrease the energy barrier of NO removal to promote deep oxidation of NO-to-NO₃⁻. This work can provide ideas for the design and preparation of the catalyst for safe photocatalytic environment purification.

In situ growth of nanoarrays on conductive substrates is an efficient strategy for designing electrocatalysts. However, preparing array with excellent catalytic activities for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) remains a challenge. Here, we construct a novel hollow sugar gourd-like Ni-Co-S@NiMoO₄·xH₂O/NF nanocage array through MOF derivation strategy for stable solar-driven overall water splitting. Due to the hollow core–shell structure and multi-component advantages, the Ni-Co-S@NiMoO₄·xH₂O/NF presents high density of active sites and fast charge transfer rate. Therefore, Ni-Co-S@NiMoO₄·xH₂O/NF exhibits attractive electrocatalytic activity in alkaline electrolytes for HER (90 mV@10 mA cm⁻²) and OER (208 mV@10 mA cm⁻², 245 mV@100 mA cm⁻²). The corresponding two-electrode electrolytic cell demonstrates small cell voltage (1.515 V @ 10 mA cm⁻²) and shows durability over 50 h at 10 mA cm⁻², exhibiting excellent overall water splitting performance. It is worth noting that the solar-assisted electrolysis cell reaches a high solar-to-hydrogen (STH) conversion rate of 19.4 %. The construction of this unique hollow structure gives a fascinating method for improving the HER and OER performance of transition metal sulfide electrocatalysts.

The 1,3-butadiene hydroesterification products, such as methyl pentenoate and dimethyl adipate, play a significant role in the production of nylon, plasticizers, and pharmaceutical intermediates. However, due to its unique π-π conjugated system, slow reaction rate, and difficulties in controlling regioselectivity, butadiene presents itself as an incredibly challenging substrate. The development of efficient and low-cost catalysts has gained substantial attention in both theoretical studies and industrial applications due to the high cost or extremely high pressure requirements. In this study, carbonyl cobalt ionic liquids were innovatively employed as catalysts to facilitate the synthesis of monoesters from hydroesterification of butadiene under mild conditions. A series of carbonyl cobalt ionic liquids with different cations were prepared and characterized for their structural properties using IR, ESI, IC, and DFT calculations. The yield of methyl pentenoate was comparable to that of Co₂CO₈ at 400 bar, and the catalysts exhibited high selectivity to methyl 3-pentenoates (>95 %), establishing a stable, efficient, and low-cost catalytic system. The experiments revealed that the type of the cation in ionic liquids remarkably influence their catalytic performance. Electrostatic potential calculations further confirmed that this performance is tightly related to the dissociation and migration behaviors of protons, leading to the proposal of a screening method for ionic liquids. In this paper, we further calculated the qualitative reaction kinetics and proposed a reaction mechanism in conjunction with previous studies. The reaction is hypothesized to begin with the formation of the active species HCo(CO)₄ by proton exchange of [HX]⁺[Co(CO)₄]⁻, in line with our experimental findings and theoretical calculations. This study presents an innovative approach to overcome the challenges associated with butadiene hydroesterification and paves the way for the development of more efficient and cost-effective catalytic systems.

Au nanoparticle catalysts are promising electrocatalysts for biomass upgrading. Starting from a pristine Au electrode, herein we demonstrate a simple route for the electrochemical preparation of Au NPs supported on thin layers of humin (Au/H). Utilizing an oxidized Au surface as a precursor, these electrocatalytic structures are formed upon reduction of 5-hydroxymethylfurfural (HMF) in alkaline media while performing a potential sweep. We subsequently utilize this Au/H structure for the electrochemical oxidation of ethanol and HMF in a rotating disk electrode (RDE) configuration and perform additional analysis via electrochemical surface-enhanced Raman Scattering (SERS). The RDE test reveals Au/H has different reaction kinetics towards alcohol and aldehyde functional groups, enabling a mechanistic understanding of the reaction pathway for HMF oxidation. The SERS experiment identifies the favorable reduction pathway from Au₂O₃ to gold, suggesting the possible active site on this catalyst for HMF oxidation.