Oxide Catalysts Research Articles

Efficient Photocatalytic Degradation of Triclosan and Methylene Blue by Synthesized Ag-Loaded ZnO under UV Light

Industrial discharge of hazardous organic and synthetic chemicals, such as antibacterials and dyes, poses severe risks to human health and the environment. This study was conducted to address the urgent need for efficient and stable zinc-oxide-based photocatalysts to degrade such pollutants. A novel approach to synthesizing silver-loaded zinc oxide (Ag@Z) catalysts was introduced by using a simple and efficient combination of hydrothermal and precipitation methods. Comprehensive characterization of Ag@Z photocatalysts was performed using XRD, XPS, Raman, UV–vis adsorption, FTIR, and SEM, revealing an enhancement of structural, optical, and morphological properties in comparison to pure zinc oxide. Notably, the 5%Ag@Z catalyst exhibited the highest degradation efficiency among the other synthesized catalysts under UV-C light irradiation, and enhanced the degradation rate of pure zinc oxide (Z) by 1.14 and 1.64 times, for Triclosan (TCS) and Methylene Blue (MB), respectively. the effect of catalyst dose and initial concentration was studied. A mechanism of degradation was proposed after investigating the effect of major reactive species. The 5%Ag@Z catalyst increased the photostability, which is a major problem of zinc oxide due to photocorrosion after reusability. We found that 50% and 74% of energy consumption for the photocatalytic degradation of TCS and MB by 5%Ag@Z, respectively, was saved in compassion with zinc oxide. The remarkable photocatalytic performance and the good recovery rate of Ag@Z photocatalysts demonstrate their high potential for photocatalytic degradation of organic contaminants in water.

Effects of MOx modification (M = Mn, Ce, and Fe) on the SCR catalytic properties of the CrOx-WOx mixed oxide catalysts

In this study, a series of MOx-modified (M = Mn, Fe, and Ce) CrOx-WOx mixed oxides were synthesized via the sol-gel technique for the selective catalytic reduction of NOx with NH3. Given the addition of MnOx or CeOx, the availability of the catalyst surface acid sites tended to decline, which negatively affected the proceeding of the deNOx process. Moreover, the retention of oxidative ability by introducing MnOx also favored the over-oxidation of NH3, which accelerated the additional formation of NOx and created a crucial barrier for the increment in the higher-temperature deNOx activity. Apparently, <80 % of the NOx could be effectively eliminated from the working gas within the whole temperature range for the CrCeW and CrMnW samples. By contrast, doping FeOx was able to introduce ample acid sites onto the catalyst surfaces, which was beneficial for the adsorption of NH3 and subsequently the facilitation of the progression of the deNOx process. Furthermore, the weakened oxidizability suppressed the over-oxidation of NH3. Consequently, a broad operating temperature window was obtained for the FeOx-doped catalyst; >90 % NOx conversion efficiency was achieved in the temperature range of 230–450 °C. During the deNOx process, the Eley-Rideal mechanism dominated over the four investigated samples.

Preparation of Nanosized Copper–Manganese Composite Oxides and Their Catalytic Performance in the Oxidation of Toluene

Nanosized Cu–Mn composite oxide catalysts were prepared from potassium permanganate, copper nitrate, n-butanol, and cetyltrimethylammonium bromide as a manganese source, copper source, reducing agent, and surfactant, respectively. The Cu[Formula: see text]–Mn sample possessed a small particle size (10–40[Formula: see text]nm) and a relatively high specific surface area ([Formula: see text]); its main components were Cu[Formula: see text]Mn[Formula: see text]O4 and Mn3O4. As a consequence, the Cu[Formula: see text]–Mn catalyst exhibited good catalytic activity in the oxidation of toluene. At a toluene concentration of 1000[Formula: see text]ppm and a space velocity of [Formula: see text], the [Formula: see text] and [Formula: see text] of the Cu[Formula: see text]–Mn catalyst toward toluene were 239[Formula: see text]C and 250[Formula: see text]C, respectively. Furthermore, even after 30[Formula: see text]h of operation at 275[Formula: see text]C, the conversion of toluene was 99% (at the space velocity of [Formula: see text]).

Bismuth Iron Oxide Catalysts for Efficient CO2 Electroreduction to Formate.

Renewable energy-driven electrocatalytic CO2 reduction reaction (CO2RR) over bismuth-based catalysts shows great promise for converting CO2 into formic acid and formate while closing the carbon cycle. Herein, we report a high-performance BiFeO3/Bi25FeO40 precatalyst, which delivers a formate partial current density of 359.8 mA cm-2 and a formate formation rate of 6.71 mmol h-1 cm-2 in a flow cell at -0.75 V versus reversible hydrogen electrode (vs RHE). Furthermore, it shows stable formate production for 88 h at -0.64 V vs RHE with a total current density of 160 mA cm-2. The impressive electrocatalytic performance toward CO2RR to formate is likely ascribed to the synergistic effect of single Bi atoms and bimetallic BiFe nanoparticles present in close proximity after in situ electrochemical reconstruction of the BiFeO3/Bi25FeO40 precatalyst. This work presents new insights into the development of highly efficient Bi-based catalysts for the CO2RR.

Renewable biomass based jet fuel: Aldol condensation of furfural with 3-pentanone over calcium zirconium mixed oxide catalyst

Furfural is a biomass-derived chemical that can be converted into different valuable chemicals using green processes. The current study deals with a highly efficient, robust, and selective solid catalyst for the aldol condensation of furfural and 3-pentanone to synthesize 1-furan-2-yl-2-methylpent-1-en-3-one under environmentally benign conditions. CaZr (different molar ratios of Ca and Zr) mixed oxide (MO) catalysts along with reference CaO and ZrO2 catalysts were prepared by the hydrothermal technique and investigated for the current reaction. Among all, CaZr (1:2) MO catalyst was found to be the best for the conversion of furfural due to its desirable basic strength with good surface area and reusability characteristics. Furfural conversion and 1-furan-2-yl-2-methylpent-1-en-3-one selectivity were found to be 94 % and 98 %, respectively, under optimized reaction conditions. Effect of various reaction parameters was studied carefully to achieve the maximum yield of the required product. Reaction mechanism and kinetics were developed. The reaction aligns with the LHHW mechanism, and the activation energy was determined to be 10.40 kcal/mol.

Synthesis of surface-engineered SrFe2O4 for efficient catalytic partial oxidation of methane

In this study, a series of platinum (Pt)-doped strontium iron oxide (SrFe2O4) catalysts with varying particle sizes were synthesized through the four different catalysis synthesis methods such as solution combustion synthesis (SCS), co-precipitation (Co-PPT), oxalic acid assisted sol-gel (OXA) and, hydrothermal (HT). The objective was to investigate the impact of particle size on the catalytic activity and long-term stability of these four catalysts. The XRD and Raman results confirmed the formation of the SrFe2O4 perovskite structure. HRTEM, SEM, and other characterizations revealed a clear correlation between the synthesis conditions and the resulting particle sizes. The highest%CH4 conversion was around 95 % for the catalyst prepared through Solution combustion synthesis and the catalyst was found to be thermally stable up to. 100 h at 800 °C with a negligible variation of conversion while maintaining the H2/CO ratio at 2.0. To gain insight into catalytic activity, stability, and selectivity of catalysts we have performed Temperature-programmed surface reaction (TPSR) at a controlled temperature ramping program. This study also includes the study of coke deposition on the spent catalysts through different characterization techniques. Furthermore, we have performed a kinetic study to find the initial rate of the reaction and the activation energy of the Pt-doped SrFe2O4 catalyst and it has been found that activation energy was 35 KJ/mol for the catalyst Pt/SrFe2O4 synthesis through the solution combustion method.

Study of Pt-modified chromium-manganese oxide alloys to improve the performance of toluene abatement

This research is dedicated to solving the environmental problems of volatile organic compounds (VOCs), particularly aromatic chemicals in industrial emissions. The research aims to explore low-temperature, effective catalytic degradation technologies, specifically involving metal oxide and noble metal oxide catalysts, especially the Cr-Mn-Pt series catalysts. The Cr-Mn-Pt catalysts synthesized by the co-precipitation method showed efficient catalytic degradation of VOCs in low-temperature environments. The results of the experiment show that the Cr-Mn-Pt catalysts achieved 90 % toluene conversion at 198 °C, a 1000 ppm toluene concentration, and GHSV=15,000 mL/g·h, which is superior to single MnOx and Cr-Mn catalysts. The catalysts are characterized in depth using X-ray diffraction, specific surface area analysis and Fourier transform infrared spectroscopy. The result shows that the high specific surface area and large volume of pores of the Cr-Mn-Pt catalyst are advantageous for enhancing their catalytic activity and stability. The catalytic mechanism analysis shows that the degradation mechanism of toluene follows the Mars-van Krevelen mechanism with the final conversion of the intermediate product benzoate to CO2 and H2O. In summary, the Cr-Mn-Pt catalyst shows great potential in the technical treatment of VOCs due to their excellent low-temperature catalytic efficiency and stability, and it has enormous practical implications for protecting the environment in the industry.

Synthesis and characterisation of mixed oxides of Co–Ni catalyst and its application in microwave mediated synthesis of Benzo[b]Pyrans

We present an easy and sustainable procedure for the productive preparation of tetrahydrobenzo[b]pyran derivatives by means of many compounds condensation of dimedon, malononitrile and several aromatic aldehydes utilizing mixed bimetallic oxides of Co–Ni as a catalyst under microwave irradiation. Present protocol involves green synthesis of mixed Co–Ni oxide catalyst using milky latex of Euphorbia neriifolia. The prepared mixed Co and Ni oxide was analyzed by X-ray diffraction (XRD), Scanning electron microscopy (SEM), Transmission electron microscopy (TEM), Fourier Transform Infra-Red Spectroscopy (FT-IR), Energy Dispersive X-ray Analysis (EDAX), X-ray Photoelectron Spectroscopy (XPS) & Brunauer-Emmett- Teller Analysis (BET). This green approach's significance is demonstrated by its one-pot synthesis, convenient without use of solvent shows good isolated yields. Multiple analytical techniques such as Fourier transform infrared spectroscopy (FT-IR), 1H and 13C nuclear magnetic resonance (NMR) spectroscopy are utilized to derive the structural properties. The mixed metal oxides of Co and Ni was found to be catalytically active and can be reused 12 times without significant loss of catalytic activity.

Features of CO₂ Hydrogenation on MoO₃/Al₂O₃ and γ-Al₂O₃

The physicochemical and catalytic (CO₂ hydrogenation) characteristics of Mo-containing catalysts have been studied. Catalysts with an oxide content of Mo 8 and 15 wt% were prepared by impregnation with ammonium paramolybdate γ-Al₂O₃ followed by drying and calcining at 500°C. The introduction of Mo oxide reduces the pore volume of the support and increases their average size, which indicates the distribution of the deposited molybdenum oxide in the pores of the support. According to X-ray diffraction data, the calcined catalyst contains practically no crystalline MoO₃ phase. According to the Raman spectra, oxygen-containing formations are present on the catalyst surface, in which Mo atoms are tetrahedrally and octahedrally coordinated with respect to oxygen atoms. The impregnated MoO₃ oxide is partially reduced by hydrogen during linear heating starting from 320°C. Hydrogenation of CO₂ (gas of composition, vol.%: 30.7 CO₂, 68 H₂, rest. N2, sample 0.5 g) was studied in the mode of linear heating up to 400°C. The main reaction is the reverse reaction of CO steam reforming. The contribution of the methanation reaction to CO₂ hydrogenation is small. An increase in temperature and pressure has a positive effect on CO₂ conversion. With an increase in pressure from 1 to 5 MPa, the CO content increases approximately twofold. In the hydrogenation of CO₂, γ-Al₂O₃, preheated in a flow of H₂ to 400°C, also exhibits noticeable activity, although significantly lower compared to Mo-containing catalysts. With increasing pressure, the activity of aluminium oxide and Mo-containing catalysts, increases.

Cobalt-Doped Ceria Sensitizer Effects on Metal Oxide Nanofibers: Heightened Surface Reactivity for High-Performing Chemiresistive Sensors.

Chemiresistive gas sensors based on semiconducting metal oxides typically rely on noble metal catalysts to enhance their sensitivity and selectivity. However, noble metal catalysts have several drawbacks for practical utilization, including their high cost, their propensity for spontaneous agglomeration, and poisoning effects with certain types of gases. As such, in the interest of commercializing the chemiresistive gas sensor technology, we propose an alternative design for a noble-metal-free sensing material through the case study of Co-doped ceria (Co-CeO2) catalysts embedded in a SnO2 matrix. In this investigation, we utilized electrospinning and subsequent calcination to prepare Co-CeO2 catalyst nanoparticles integrated with SnO2 nanofibers (NFs) with uniform particle distribution and particle size regulation down to the sub-2 nm regime. The resulting Co-CeO2@SnO2 NFs exhibited superior gas sensing characteristics toward isoprene (C5H8) gas, a significant biomarker for monitoring the onset of various diseases through breath diagnostics. In particular, we identified that the Co-CeO2 catalysts, owing to the transition metal doping, facilitated the spillover of chemisorbed oxygen species to the SnO2 sensing body. This resulting in the sensor having a 27.4-fold higher response toward 5 ppm of C5H8 (compared to pristine SnO2), exceptionally high selectivity, and a low detection limit of 100 ppb. The sensor also exhibited high stability for prolonged response-recovery cycles, attesting to the strong anchoring of Co-CeO2 catalysts in the SnO2 matrix. Based on our findings, the transition metal-doped metal oxide catalysts, such as Co-CeO2, demonstrate strong potential to completely replace noble metal catalysts, thereby advancing the development of the commercially viable chemiresistive gas sensors free from noble metals, capable of detecting target gases at sub-ppm levels.

Effect of Mn or Fe on CrMoOx /TiO2 selective catalytic reduction catalyst

Developing a high-efficiency catalyst with both superior low-temperature activity and good sulfur and water resistance is still challenging for the NH3 selective catalytic reduction (SCR). Herein, a series of Mn- and Fe-doped CrMoOx/TiO2 catalysts were elaborately designed and the Cr3Mo6Mn2/TiO2 catalyst exhibits the best NOx conversion rate, reaching 81. 8 % at 90 ℃ and closing to 100 % at 150 ℃, and the NOx conversion reach ∼71 % at 150 ℃ for 30 h in presence of H2O+SO2. A series of characterization studies revealed that the abundance of Lewis acidic sites on the catalysts and the protective effect of Mo are conducive to the enhancement of SO2+H2O resistance. cr3Mo6Mn2/TiO2 dominates the SCR reaction through the Eley-Rideal (E-R) pathway between adsorbed NH4+/NH3 and gaseous NOx, generating N2 and H2O. This work provides a new strategy for improving the tolerance of chromium-based oxide catalysts to sulfur dioxide and water at low temperatures.

Atomic-Level Observation of Potential-Dependent Variations at the Surface of an Oxide Catalyst during Oxygen Evolution Reaction.

Understanding the intricate details of the surface atomic structure and composition of catalysts during the oxygen evolution reaction (OER) is crucial for developing catalysts with high stability in water electrolyzers. While many notable studies highlight surface amorphization and reconstruction, systematic analytical tracing of the catalyst surface as a function of overpotential remains elusive. Heteroepitaxial (001) films of chemically stable and lattice-oxygen-inactive LaCoO3 are thus utilized as a model catalyst to demonstrate a series of atomic-resolution observations of the film surface at different anodic potentials. The first key finding is that atoms at the surface are fairly dynamic even at lower overpotentials. Angstrom-scale atomic displacements within the perovskite framework are identified below a certain potential level. Another noteworthy feature is that amorphization (or paracrystallization) with no long-range order is finally induced at higher overpotentials. In particular, surface analyses consistently support that the oxidation of lattice oxygen is coupled with amorphous phase formation at the high potentials. Theoretical calculations also reveal an upward shift of oxygen 2p states toward the Fermi level, indicating enhanced lattice oxygen activation when atom displacement occurs more extensively. This study emphasizes that the degradation behavior of OER catalysts can distinctively vary depending on the overpotential level.

Facile preparation of alkali metal‐modified hollow nanotubular manganese‐based oxide catalysts and their excellent catalytic soot combustion performance

AbstractThe soot emitted during the operation of diesel engine exhaust seriously threatens the human health and environment, so treating diesel engine exhaust is critical. At present, the most effective method for eliminating soot particles is post‐treatment technology. Preparation of economically viable and highly active soot combustion catalysts is a pivotal element of post‐treatment technology. In this study, different single‐metal oxide catalysts with fibrous structures and alkali metal‐modified hollow nanotubular Mn‐based oxide catalysts were synthesized using centrifugal spinning method. Activity evaluation results showed that the manganese oxide catalyst has the best catalytic activity among the prepared single‐metal oxide catalysts. Further research on alkali metal modification showed that doping alkali metals is beneficial for improving the oxidation state of manganese and generating a large number of reactive oxygen species. Combined with the structural effect brought by the hollow nanotube structure, the alkali metal‐modified Mn‐based oxide catalysts exhibit superior catalytic performance. Among them, the Cs‐modified Mn‐based oxide catalyst exhibits the best catalytic performance because of its rich active oxygen species, excellent NO oxidation ability, abundant Mn4+ ions (Mn4+/Mnn+ = 64.78%), and good redox ability. The T10, T50, T90, and CO2 selectivity of the Cs‐modified Mn‐based oxide catalyst were 267°C, 324°C, 360°C, and 97.8%, respectively.

Synthesis of acetonitrile from NH3/syngas mixtures on molybdenum nitride: Insights into the reaction mechanism

Owing to their metallic-like surface electronic properties and their capacity to act as reservoirs and solid transfer agents for active nitrogen, transition metal nitrides are interesting as solid catalysts for C-C and C-N coupling reactions for the bottom-up production of higher (C2+) nitrogenated chemicals from unconventional carbon resources. The catalytically active state and reaction mechanism for the direct synthesis of acetonitrile from syngas/ammonia mixtures are studied on an unsupported Mo catalyst from complementary experimental and computational approaches. Temperature resolved X-ray diffraction and X-ray photoemission spectroscopy verify that an oxidic MoO3 catalyst precursor undergoes in situ (near-surface) nitridation, upon exposure to reaction conditions at 723 K, rendering Mo2N the actual working catalyst. Density Functional Theory mechanistic investigations on a γ-Mo2N(100) model surface point to a hydrogen-assisted CO dissociation on the nitride surface. Moreover, surface oxygen, evolved from CO dissociation, is predicted to play a central role as hydrogen acceptor, to enable the dehydrogenative NH3 dissociation. Direct condensation of CH and N adspecies proceeds with a low energy barrier of 33 kJ mol−1, which makes C-N coupling preferred over full hydrogenation of CHx species, in agreement with the experimental modest selectivity to methane (ca. 10 %). Both experimental and computational results indicate that HCN is a major intermediate product along the reaction pathway to acetonitrile. No energetically feasible associative reaction pathways could be identified for C-C coupling from HCN. The dissociation of the latter intermediate product is predicted to precede the reaction of CN adspecies to CHx. Similarly to NH3 dissociation, dehydrogenative HCN activation on the Mo2N surface is predicted to be facilitated through hydrogen abstraction by surface oxygen species, yet subjected to a comparatively higher energy barrier (>120 kJ mol−1), therefore likely to control the overall kinetics. These findings suggest that the enhancement of HCN dissociation is a central design objective towards Mo2N-based catalysts with advanced performance.

Elucidating the local structure and electronic properties of a highly active overall alkaline water splitting NixCo1-xO/hollow carbon sphere catalyst

A NixCo1-xO/HCS catalyst with superior water-splitting is presented. High water-splitting reaction kinetics and enhanced durability were observed. The structure-function relationship was investigated with XPS, which demonstrated the presence of dominant Ni2+ and Co2+ species and a functionalized HCS support where nucleation of small metal oxide nanoparticles occurred. The PDF showed broadened Nickel/Cobalt-oxide bonds and expansion of the metal-metal pair distances. The alteration of the Metal-Oxide and Metal-Metal-Oxide bonds favored better HER and OER electrocatalysis, also as supported by DFT. EXAFS showed the existence of the bimetallic oxide catalyst and the stretching of the Ni–O bonds due to the coordination of the Ni–O with the Co. The composite exhibited higher activity and enhanced electrocatalytic mechanism towards water splitting through higher exchange current densities (0.615 and 0.886 mA cm−2) and low charge transfer resistance (14 and 10 Ω) respectively. Chronoamperometry proved the catalyst's stability during prolonged electrolysis.

Manganese-rhodium nanoparticles: Adsorption on titanium oxide surfaces and catalyst for syngas reactions.

Manganese-rhodium (Mn-Rh) nanoparticles have emerged as a promising candidate for catalytic applications in the production of syngas, a critical precursor for a wide range of industrial processes. This study employs a comprehensive, theoretical, and computational approach to investigate the structural and electronic properties of Mn-Rh nanoparticles, with a specific focus on their interaction with titanium oxide (TiO2) surfaces and their potential as catalysts for syngas reactions. The density functional theory calculations are employed to explore the adsorption behavior of Mn-Rh nanoparticles on TiO2 surfaces. By analyzing the adsorption energies, geometries, and electronic structure at the nanoscale interface, we provide valuable insights into the stability and reactivity of Mn-Rh nanoparticles when immobilized on TiO2 supports. Furthermore, the catalytic performance of Mn-Rh nanoparticles in syngas production is thoroughly examined. Through detailed reaction mechanism studies and kinetic analysis, we elucidate the role of Mn and Rh in promoting syngas generation via carbon dioxide reforming and partial oxidation reactions. The findings demonstrate the potential of Mn-Rh nanoparticles as efficient catalysts for these crucial syngas reactions. This research work not only enhances our understanding of the fundamental properties of Mn-Rh nanoparticles but also highlights their application as catalysts for sustainable and industrially significant syngas production.

Stable production of hydrogen peroxide over zinc oxide @ zeolitic imidazolate Framework-8 composite catalysts

A promising method of producing hydrogen peroxide (H2O2) is the electrochemical two-electron water oxidation reaction (2e− WOR). In this process, it is important to design electrocatalysts that are both earth abundant and environmentally friendly, as well as offering high stability and production rates. The research of WOR catalysts, such as the extensively used transition metal oxides, is mainly focused on the modification of transition metal elements. Few studies pay attention to the protective heterostructure of metal oxides. Here, we demonstrate for the first time an organometallic skeleton protection strategy to develop highly stable WOR catalysts for H2O2 generation. Unlike the pure ZnO and zeolite imidazole framework-8 (ZIF-8) catalysts, ZnO@ZIF-8 enabled the production of hydrogen peroxide at high voltages. The experimental results demonstrate that the ZnO@ZIF-8 catalyst stably generates H2O2 even under a high voltage of 3.0 V vs. RHE, with a yield reaching 2845.819 μmolmin−1 g−1. ZnO@ZIF-8 shows a relatively low overpotential, with a current density of 10 mA cm−2 and an overpotential of 110 mV. The ZnO@ZIF-8 catalyst’s maximal FE value was 4.72 %. Moreover, the ZnO@ZIF-8 catalyst exhibits remarkable durability even after an extended 60-hour stability test. Operando Raman and theoretic calculation analyses reveal that the metal–organic skeleton being encapsulated on the metal oxide surface synergizes with each other, not only expanding the electrochemical surface area, but also adjusting the catalyst metal sites’ adsorption capacity. A novel approach to the modification of 2e− WOR metal oxide catalyst is presented in this work.

RuNi/TiZr-MMO Catalysts Derived from Zr-Modified NiTi-LDH for CO-Selective Methanation.

CO-selective methanation (CO-SMET) is an efficient hydrogen-rich (H2-rich) gas purification technology for proton exchange membrane fuel cells. It is vital to develop suitable catalysts with good low-temperature activity for CO-SMET reactions. In this study, RuNi/TiZrx-mixed metal oxide (RuNi/TiZrx-MMO) catalysts with different molar ratios of Zr/Ti, derived from a Zr-promoted NiTi-layered double hydroxide (NiTi-LDH) precursor were successfully prepared using the co-precipitation and wet impregnation methods. The RuNi/TiZr0.2-MMO catalyst possesses higher catalytic performance in a lower temperature window of 180-280 °C, which can reduce the CO concentration to be below 10 ppm. The characterization results obtained from XRD, BET, SEM, TEM, XPS, TPR, and TPD suggest that the addition of ZrO2 increases the surface area of the catalyst, improves the dispersion of metallic nanoparticles, increases the reducibility of Ni species on the RuNi/TiZr0.2-MMO catalyst's surface, and enhances the adsorption and activation ability of CO, resulting in remarkable catalytic performance at lower reaction temperatures. Moreover, the RuNi/TiZr0.2-MMO catalyst demonstrated long-term catalytic stability and carbon resistance.

Solvent‐Free Efficient Hydrogenation of Levulinic Acid over Silicotungstic Acid Promoting the Activity of CuNiAl Catalysts: A Synergistic Effect

AbstractMulti‐metallic catalysts rely on the synergistic effect between metals to perform better catalytic effect in biomass hydrogenation experiments compared with mono‐metallic catalysts. A series of CuNiAl composite metal oxide catalysts promoted by silicotungstic acid (HSiW), which were prepared by co‐precipitation and impregnation methods, were characterized by powder X‐ray diffraction (XRD), N2‐physisorption, scanning electron microscope (SEM) and NH3 program temperature desorption (NH3‐TPD) and pyridine infrared adsorption (Py‐FTIR). Their catalytic performance was evaluated in the hydrogenation of levulinic acid (LA) to prepare γ‐valerolactone (GVL). The results showed that the addition of Cu could improve the hydrogenation activity of Ni, and the addition of HSiW could further increase the amount of acid sites in the catalysts. Both of them could enhance the conversion of LA to some extent. CuNiAl‐5SiW, the par excellence catalyst, relied on the synergistic interactions between metals as well as the Brønsted and Lewis acid active sites to show efficient hydrogenation performance. The CuNiAl‐5SiW catalyst demonstrated 96.9 % conversion of LA and more than 99 % selectivity to GVL under 2 hours of reaction time, 180 °C of reaction temperature, 3.0 MPa of initial hydrogen pressure and solvent‐free conditions.

Electrocatalytic Upgrading of Plastic and Biomass-Derived Polyols to Formamide under Ambient Conditions.

Electrocatalytic upgrading of wasted plastic and renewable biomass represents a sustainable method to produce chemicals but is limited to carbohydrates, leaving other value-added chemicals, such as organonitrogen compounds, being scarcely explored. Herein, we reported an electrocatalytic oxidation strategy to transform polyethylene terephthalate (PET) plastic-derived ethylene glycol (EG) and biomass-derived polyols into formamide, in the presence of ammonia (NH3) over a tungsten oxide (WO3) catalyst. Taking EG-to-formamide as an example, we achieved a high formamide productivity of 537.7 μmol cm-2 h-1 with FE of 43.2 % at a constant current of 100 mA cm-2 in a flow electrolyzer with 12-h test, representing a more advantageous performance compared with previous reports for formamide electrosynthesis. Mechanistic understanding revealed that the cleavage of the C-C bond in the EG was facilitated by nucleophilic attack of in situ formed nitrogen radicals from NH3, with resultant C-N bond construction and eventually formamide production. Furthermore, this strategy can be extended to transformation of PET bottle and a series of biomass-derived polyols with carbon number from three (glycerol) to six (glucose), producing formamide with high efficiencies. This work demonstrates a sustainable upgrading strategy of plastic and biomass that may have implications to more value-added chemicals production beyond carbohydrates.