PO4 3- Coordinated Robust Single-Atom Platinum Catalyst for Selective Polyol Oxidation

Effect of Pt Nanoparticle Morphology on the Aerobic Oxidation of Ethylene Glycol to Glycolic Acid in Water

Pt nanoparticles (diameter <3 nm), generated by metal vapor synthesis and supported on a high surface area carbon, were used to catalyze the aerobic oxidation of ethylene glycol to glycolic acid (GA) in water under neutral and basic reaction conditions. Controlled heat treatment of the catalyst under a nitrogen atmosphere brought about the formation of a morphologically well-defined catalyst. A combination of atomic resolution electron microscopy, CO stripping voltammetry, and XPS analyses conducted on as-synthesized and heat-treated catalysts demonstrated the crucial role of the nanoparticles' morphology on the stabilization of catalytically highly active Pt-OH surface species, which were key species for the Pt-catalyzed oxidation of the alcohol to the carbonyl functionality. The boosting effect of base on the catalyst' s activity and GA selectivity has been proved experimentally (autoclave experiments). The effect of base on the nonmetal-catalyzed reaction steps (i.e., aerobic oxidation of carbonyl to acid functionality) has been proved by DFT calculations.

Revealing OH species in situ generated on low-valence Cu sites for selective carbonyl oxidation

Catalytic oxidation through the transfer of lattice oxygen from metal oxides to reactants, namely the Mars-van Krevelen mechanism, has been widely reported. In this study, we evidence the overlooked oxidation route that features the in situ formation of surface OH species on Cu catalysts and its selective addition to the reactant carbonyl group. We observed that glucose oxidation to gluconic acid in air (21% O2) was favored on low-valence Cu sites according to X-ray spectroscopic analyses. Molecular O2 was activated in situ on Cu0/Cu+ forming localized, adsorbed hydroxyl radicals (*OH) which played the primary reactive oxygen species as confirmed by the kinetic isotope effect (KIE) study in D2O and in situ Raman experiments. Combined with DFT calculations, we proposed a mechanism of O2-to-*OH activation through the *OOH intermediate. The localized *OH exhibited higher selectivity toward glucose oxidation at C1HO to form gluconic acid (up to 91% selectivity), in comparison with free radicals in bulk environment that emerged from thermal, noncatalytic hydrogen peroxide decomposition (40% selectivity). The KIE measurements revealed a lower glucose oxidation rate in D2O than in H2O, highlighting the role of water (H2O/D2O) or its derivatives (e.g., *OH/*OD) in the rate-determining step. After proving the C1-H activation step kinetically irrelevant, we proposed the oxidation mechanism that was characterized by the rate-limiting addition of *OH to C1=O in glucose. Our findings advocate that by maneuvering the coverage and activity of surface *OH, high-performance oxidation of carbonyl compounds beyond biomass molecules can be achieved in water and air using nonprecious metal catalysts.

Surface coordination induced a quasi p-n junction for efficient visible light driven degradation of tetracycline over hydroxyapatite

The removal of antibiotics from aquatic solutions remains a global environmental challenge. In this work, the photocatalytic removal of a typical antibiotic-tetracycline (TC) using hydroxyapatite (HAp) as a catalyst was investigated. It was impressive that TC could be efficiently degraded by HAp under visible light irradiation, even though both HAp and TC exhibited poor harvesting in visible light region. The experimental and theoretical explorations were undertaken to thoroughly investigate the underlying mechanism of visible light degradation of TC over HAp. The results indicated that the formed TC-HAp complexes via surface coordination played an important role as photosensitizers for the visible light response. Together with the formation of a quasi p-n junction via band alignment, the photogenerated electrons in the highest unoccupied molecular orbital (HOMO) of TC-HAp were excited to the lowest unoccupied molecular orbital (LUMO) and subsequently migrated to the conduction band of HAp to achieve the efficient charge separation. Superoxide radicals and holes were found to be the major active species for TC degradation. The toxicity evaluation showed that TC could be transferred to the lower toxic intermediates, and deep oxidation with prolonged reaction time was necessary to eliminate the toxicity of TC. This work demonstrates the surface coordination with subsequent quasi p-n junction mechanism of TC degradation over HAp under visible light, which will stimulate us to explore new efficient photocatalytic systems for the degradation of various contaminants.

Toward Functionality and Deactivation of Metal-Single-Atom in Heterogeneous Photocatalysts

Single-atom heterogeneous catalysts (SAHCs) provide an enticing platform for understanding catalyst structure-property-performance relationships. The 100% atom utilization and adjustable local coordination configurations make it easy to probe reaction mechanisms at the atomic level. However, the progressive deactivation of metal-single-atom (MSA) with high surface energy leads to frequent limitations on their commercial viability. This review focuses on the atomistic-sensitive reactivity and atomistic-progressive deactivation of MSA to provide a unifying framework for specific functionality and potential deactivation drivers of MSA, thereby bridging function, purpose-modification structure-performance insights with the atomistic-progressive deactivation for sustainable structure-property-performance accessibility. The dominant functionalization of atomically precise MSA acting on properties and reactivity encompassing precise photocatalytic reactions is first systematically explored. Afterward, a detailed analysis of various deactivation modes of MSA and strategies to enhance their durability is presented, providing valuable insights into the design of SAHCs with deactivation-resistant stability. Finally, the remaining challenges and future perspectives of SAHCs toward industrialization, anticipating shedding some light on the next stage of atom-economic chemical/energy transformations are presented.

Revealing Hydrogen Bond Effect in Rechargeable Aqueous Zinc-Organic Batteries

The surrounding hydrogen bond (H-bond) interaction around the active sites plays indispensable functions in enabling the organic electrode materials (OEMs) to fulfill their roles as ion reservoirs in aqueous zinc-organic batteries (ZOBs). Despite important, there are still no works could fully shed its real effects light on. Herein, quinone-based small molecules with a H-bond evolution model has been rationally selected to disclose the regulation and equilibration of H-bond interaction between OEMs, and OEM and the electrolyte. It has been found that only a suitable H-bond interaction could make the OEMs fully liberate their potential performance. Accordingly, the 2,5-diaminocyclohexa-2,5-diene-1,4-dione (DABQ) with elaborately designed H-bond structure exhibits a capacity of 193.3 mAh g-1 at a record-high mass loading of 66.2 mg cm-2 and 100 % capacity retention after 1500 cycles at 5 A g-1. In addition, the DABQ//Zn battery also possesses air-rechargeable ability by utilizing the chemistry redox of proton. Our results put forward a specific pathway to precise utilization of H-bond to liberate the performance of OEMs.

Ultrasonic irradiation-assisted MnFe2O4 nanoparticles catalyzed solvent-free selective oxidation of benzyl alcohol to benzaldehyde at room temperature

Magnetic nanoparticles (NPs) play a vital role in heterogeneous catalysis because of their easy separation, and effective recyclability. Herein, we report the synthesis of MnFe2O4 NPs for use as catalysts in the selective oxidation of benzyl alcohol to benzaldehyde under mild conditions. The MnFe2O4 NPs have been synthesized by precipitation method followed by hydrothermal ageing at 180 °C for 4.0 h. We have investigated the effect of chitosan and carboxymethyl cellulose on the size or morphology of the formed MnFe2O4 NPs. The X-ray diffraction study confirms the formation of pure and crystalline MnFe2O4 with varying average crystallite sizes ranging from 18 to 28 nm based on the type of additive used. The electron microscopy study reveals that the additive plays a significant role in controlling the morphology of the formed MnFe2O4 NPs. These MnFe2O4 NPs exhibit superparamagnetic behaviour at room temperature and can effectively catalyze the solvent-free selective oxidation of benzyl alcohol to benzaldehyde in the presence of tert-butyl hydroperoxide at room temperature under ultrasonic irradiation. The developed protocol can be extended to various substituted benzyl alcohols having both the electron withdrawing and electron donating groups to afford moderate to excellent yield of the products. The catalyst is magnetically retrievable, highly stable, and can be reused up to the sixth run without significant loss of catalytic activity.

Catalytic Linkage Engineering of Covalent Organic Frameworks for the Oxygen Reduction Reaction

Metal-free covalent organic frameworks (COFs) have been employed to catalyze the oxygen reduction reaction (ORR). To achieve high activity and selectivity, various building blocks containing heteroatoms and groups linked by imine bonds were used to create catalytic COFs. However, the roles of linkages of COFs in ORR have not been investigated. In this work, the catalytic linkage engineering has been employed to modulate the catalytic behaviors. To create single catalytic sites while avoiding other possible catalytic sites, we synthesized COFs from benzene units linked by various bonds, such as imine, amide, azine, and oxazole bonds. Among these COFs, the oxazole-linkage in COFs enables to catalyze the ORR with the highest activity, which achieved a half-wave potential of 0.75 V and a limited current density of 5.5 mA cm-2 . Moreover, the oxazole-linked COF achieved a conversion frequency (TOF) value of 0.0133 S-1 , which were 1.9, 1.3, and 7.4-times that of azine-, amide- and imine-COFs, respectively. The theoretical calculation showed that the carbon atoms in oxazole linkages facilitated the formation of OOH* and promoted protonation of O* to form the OH*, thus advancing the catalytic activity. This work guides us on which linkages in COFs are suitable for ORR.

Highly Selective Activation of C-H Bond and Inhibition of C-C Bond Cleavage by Tuning Strong Oxidative Pd Sites

Improving the product selectivity meanwhile restraining deep oxidation still remains a great challenge over the supported Pd-based catalysts. Herein, we demonstrate a universal strategy where the surface strong oxidative Pd sites are partially covered by the transition metal (e. g., Cu, Co, Ni, and Mn) oxide through thermal treatment of alloys. It could effectively inhibit the deep oxidation of isopropanol and achieve the ultrahigh selectivity (>98%) to the target product acetone in a wide temperature range of 50-200 °C, even at 150-200 °C with almost 100% isopropanol conversion over PdCu_1.2/Al₂O₃, while an obvious decline in acetone selectivity is observed from 150 °C over Pd/Al₂O₃. Furthermore, it greatly improves the low-temperature catalytic activity (acetone formation rate at 110 °C over PdCu_1.2/Al₂O₃, 34.1 times higher than that over Pd/Al₂O₃). The decrease of surface Pd site exposure weakens the cleavage for the C-C bond, while the introduction of proper CuO shifts the d-band center (ε_d) of Pd upward and strengthens the adsorption and activation of reactants, providing more reactive oxygen species, especially the key super oxygen species (O₂^-) for selective oxidation, and significantly reducing the barrier of O-H and β-C-H bond scission. The molecular-level understanding of the C-H and C-C bond scission mechanism will guide the regulation of strong oxidative noble metal sites with relatively inert metal oxide for the other selective catalytic oxidation reactions.

Single-atom catalysts for hydroformylation of olefins

Hydroformylation is one of the most significant homogeneous reactions. Compared with homogeneous catalysts, heterogeneous catalysts are easy to be separated from the system. However, heterogeneous catalysis faces the problems of low activity and poor chemical/regional selectivity. Therefore, there are theoretical and practical significance to develop efficient heterogeneous catalysts. SACs can be widely applied in hydroformylation in the future, due to the high atom utilization efficiency, stable active sites, easy separation, and recovery. In this review, the recent advances of SACs for hydroformylation are summarized. The regulation of microstructure affected on the reactivity, stability of SACs, and chem/regioselectivity of SACs for hydroformylation are discussed. The support effect, ligand effect, and electron effect on the performance of SACs are proposed, and the catalytic mechanism of SACs is elaborated. Finally, we summarize the current challenges in this field, and propose the design and research ideas of SACs for hydroformylation of olefins.

Collaborative Purification of Tert-Butanol and N2O over Fe/Co-Zeolite Catalysts

N₂O is a greenhouse gas and a candidate oxidant. Volatile organic pollutants (VOCs) have caused great harm to the atmospheric ecological environment. Developing the technique utilizing N₂O as the oxidant to oxidize VOCs to realize the collaborative purification has significant importance and practical value for N₂O emission control and VOC abatement. Therefore, the study of N₂O catalytic oxidation of tert-butanol based on zeolite catalysts was carried out. A series of molecular sieves, including FER, MOR, ZSM-5, Y, and BEA, were selected as the catalyst objects, and the 1.5% wt Fe and Co were, respectively, loaded on the zeolite catalysts via the impregnation method. It was found that the catalytic performance of BEA was the best among the molecular sieves. Comparing the catalytic performance of Fe-BEA under different load gradients (0.25~2%), it was found that 1.5% Fe-BEA possessed the best catalytic activity. A series of characterization methods showed that Fe³⁺ content in 1.5% Fe-BEA was the highest, and more active sites formed to promote the catalytic reaction. The α-O in the reaction eventually oxidized tert-butanol to CO₂ over the active site. The Co mainly existed in the form of Co²⁺ cations over Co-BEA samples; the 2% Co-BEA possessing higher amounts of Co²⁺ exhibited the highest activity among the prepared Co-BEA samples.

Concerted and Selective Electrooxidation of Polyethylene-Terephthalate-Derived Alcohol to Glycolic Acid at an Industry-Level Current Density over a Pd-Ni(OH)2 Catalyst

Electro-reforming of Polyethylene-terephthalate-derived (PET-derived) ethylene glycol (EG) into fine chemicals and H₂ is an ideal solution to address severe plastic pollution. Here, we report the electrooxidation of EG to glycolic acid (GA) with a high Faraday efficiency and selectivity (>85 %) even at an industry-level current density (600 mA cm^-2 at 1.15 V vs. RHE) over a Pd-Ni(OH)₂ catalyst. Notably, stable electrolysis over 200 h can be achieved, outperforming all available Pd-based catalysts. Combined experimental and theoretical results reveal that 1) the OH* generation promoted by Ni(OH)₂ plays a critical role in facilitating EG-to-GA oxidation and removing poisonous carbonyl species, thereby achieving high activity and stability; 2) Pd with a downshifted d-band center and the oxophilic Ni can synergistically facilitate the rapid desorption and transfer of GA from the active Pd sites to the inactive Ni sites, avoiding over-oxidation and thus achieving high selectivity.

Alkali and Alkaline Earth Metals (K, Ca, Sr) Promoted Cu/SiO2 Catalyst for Hydrogenation of Methyl Acetate to Ethanol

The advancing effects of various alkali and alkaline earth metals (inclusive of K, Ca, and Sr) modified Cu/SiO2 catalysts, prepared with a modified precipitation-gel method, were investigated for the production of ethanol via hydrogenation of methyl acetate. Our results showed that Sr-doped catalysts exhibited the best and most consistent results during catalytic tests. A series of techniques, including X-ray diffraction technique, Raman spectroscopy, N2 adsorption/desorption, N2O titration method, FTIR spectroscopy, and H2 temperature, programmed desorption and reduction (TPD and TPR), and X-ray Photoelectron Spectroscopy, which was used to check the detailed characterization of Sr modification in the catalyst and its structural impacts on the properties of the catalyst. These results demonstrated that the addition of 5%Sr could strengthen the intrinsic stability of the catalyst by formulating the appropriate ratio of Cu+/(Cu0 + Cu+) to facilitate catalytic outcome improvement. The addition of 5%Sr-30%Cu/SiO2 under the most favorable conditions, resulting in the peak conversion of MA (95%) and ethanol selectivity (96%), indicates its magnificent catalytic stabilizing effects. Furthermore, the best performing catalyst was compared and tested under various conditions (LHSV and temperatures) and a 300 h long life run.

The technical and economic analysis of processing and conversion of heavy oil cuts to valuable refinery products

Many of the modern refineries are founded on converting/upgrading the heavy bases of low value to lighter products by higher added value like gasoline, jet fuel and diesel fuel. In this work, some process configurations in heavy refinery cracking, converting and treating are technically and economically evaluated. In this purpose, four process configurations for refinery plants are suggested. These processes are evaluated and analyzed to obtain the most optimal configurations with the aim of achieving the most valuable refinery products. The difference of the processes is in heavy residue conversion and processing. These processes are included the Asphalt Air Blowing Unit (AABU, Type 1), Delayed Coker Unit (DCU, Type 2), Heavy Residue Hydro-Conversion (HRH, Type 3) and Solvent De-Asphalting (SDA, Type 4). The units are common in mentioned refineries cases and just ABU, HCU, DCU, HRH and SDA are different. In economic consideration, the payout period is considered as one of the standard methods of assessing the economic projects and economically estimating them. As results, the highest rate of gasoline is recorded in the refinery type of DCU unit and the highest amount of LPG/C4/C3, kerosene and gasoline production observed in refinery type of HRH unit. The construction of refinery with ABU unit has minimum investment (980 million $) and highest rate of return (19.4).

Synergetic Dual-Site Atomic Catalysts for Sensitive Chemiluminescent Immunochromatographic Test Strips

In view of the outstanding catalytic efficiency, single-atom catalysts (SACs) have shown great promise for the construction of sensitive chemiluminescent (CL) platforms. However, the low loading amount of active sites dramatically obstructs the improved catalytic activity of these metal SACs. Benefiting from the exceedingly unique catalytic properties of the metal-metal bonds, atomic clusters may give rise to enhancing the catalytic properties of SACs based on the synergistic effects of dual atomic-scale sites. Inspired by this, atomic Co₃N clusters-assisted Co SACs (Co₃N@Co SACs) were synthesized through a facile doping method. Through X-ray absorption spectroscopy, the active metal sites in the synergetic dual-site atomic catalysts of Co₃N@Co SACs were confirmed to be Co-O₄ and Co₃-N moieties. Co₃N@Co SACs served as a superior co-reactant to remarkably enhance the luminol CL signal by 2155.0 times, which was prominently superior to the boosting effect of the pure Co SACs (98.4 times). The synergetic dual-site atomic catalysts contributed to accelerating the decomposition of H₂O₂ into singlet oxygen as well as superoxide radical anions to display superb catalytic performances. For a concept employment, Co₃N@Co SACs were attempted to utilize as CL probes for establishing a sensitive immunochromatographic assay to quantitate pesticide residues, in which imidacloprid was adopted as the model analyte. The quantitative range of imidacloprid was 0.05-10 ng mL^-1 with a detection limit of 1.7 pg mL^-1 (3σ). Furthermore, the satisfactory recovery values in mock herbal medicine samples demonstrated the effectiveness of the proposed Co₃N@Co SAC-based CL platform. In the proof-of-concept work, synergetic dual-site atomic catalysts show great perspectives on trace analysis and luminescent biosensing.