Catalysts For Conversion Research Articles

Freestanding Penta-Twinned Palladium Nanosheets.

Control over the morphology of nanomaterials to have a 2D structure and manipulating the surface strain of nanostructures through defect control have proved to be promising for developing efficient catalysts for sustainable chemical and energy conversion. Here a one-pot aqueous synthesis route of freestanding Pd nanosheets with a penta-twinned structure (PdPT NSs) is presented. The generation of the penta-twinned nanosheet structure can be succeeded by directing the anisotropic growth of Pd under the controlled reduction kinetics of Pd precursors. Experimental and computational investigations showed that the surface atoms of the PdPT NSs are effectively under a compressive environment due to the strain imposed by their twin boundary defects. Due to the twin boundary-induced surface strain as well as the 2D structure of the PdPT NSs, they exhibited highly enhanced electrocatalytic activity for oxygen reduction reaction compared to Pd nanosheets without a twin boundary, 3D Pd nanocrystals, and commercial Pd/C and Pt/C catalysts.

A Theoretical Study on the 1,2-Bis-Silylation of Internal Alkynes Catalyzed by Ni-NHC: Understanding the Influential Factors on Catalyst Conversion, Stability, and Reactivity

A Theoretical Study on the 1,2-Bis-Silylation of Internal Alkynes Catalyzed by Ni-NHC: Understanding the Influential Factors on Catalyst Conversion, Stability, and Reactivity

NNO donor Schiff base metal complexes: Enzyme mimicking, DNA binding and biological insights

The present work focuses on the microwave-assisted synthesis, characterization and biological applications of a novel tridentate NNO donor Schiff base ligand derived from the condensation of 4-(Diethylamino)salicylaldehyde and 4,5-Dimethyl-1,2-phenylenediamine, along with its transition metal complexes of Cu(II) and Co(II) in 1:1 and 1:2 ratios each respectively. A theoretical basis for comprehending the electronic framework and characteristics of the complexes has been studied through the use of a computational approach. Further, the distorted octahedral geometry of the Schiff base metal complexes is confirmed by using analytical methods such as elemental analysis, molar conductance, ESI-MS, UV–Vis, FTIR, TGA and NMR spectra, which confirmed that NNO donor site of the ligand is coordinated with the metal ions. The complexes have been screened for their potential application as a catalyst for the catalytic conversion of 3,5-di‑tert‑butyl‑catechol (3,5-DTBC) to 3,5-di‑tert-butylquinone (3,5-DTBQ) and the turnover numbers (Kcat) have been found in the range 36.46–43.05 h−1 in methanol. Absorption spectroscopic technique has been employed to examine the possible modalities of interactions with the synthesized complexes using CT-DNA and the related binding constants exhibited in the range 2.58 × 104 M−1 to 1.98 × 105 M−1 thus depicting appreciable binding affinity. To evaluate the bioactivities, in-vitro assays for anti-oxidant and anti-inflammatory activity have also been implemented. The Cu(II) complex (CuL) has significant anti-oxidant activity and the Co(II) complex (CoL) has superior anti-inflammatory activity compared to all other complexes with IC50 values of 238.78 µM and 140.25 µM respectively. To better understand the molecular-level interactions and identify probable binding energies of inhibitors, molecular docking simulations have been performed.

Implanting multi-functional ionic liquids into MOF nodes for boosting CO2 cycloaddition under solventless and cocatalyst-free conditions

It is critical to design an effective catalyst for CO2 conversion into cyclocarbonate to achieve the carbon neutrality. Herein, MIL-101(Cr) tethered by hydrogen bond donors (HBD)-containing ionic liquids (denoted as MIL-101-ILs(R), R = OH, NH2, and COOH) were synthesized through the implantation of 4,4′-bipyridine into MOF nodes via the post-synthetic modification, followed by the decoration with bromoalkanes including bromoethanol, bromoethylamine, and bromoacetic acid. Their catalytic performance were evaluated by the epoxide cycloaddition reaction under 1.0 MPa CO2 and 80 ℃ for 6 h in the absence of solvent and cocatalyst. Compared to MIL-101-ILs without HBD, MIL-101-ILs(OH) and MIL-101-ILs(NH2) demonstrated the more chloropropene carbonate (CPC) yield of 88 % and 83 %, respectively. Notably, MIL-101-ILs(COOH) exhibited an uppermost activity with a CPC yield of 96 %, attributed to the cooperativity of Lewis acidity originating from Cr3O clusters, hydrogen-bond interaction afforded by carboxyl groups, and the strong nucleophilicity offered by Br- ions of ILs. Moreover, MIL-101-ILs(COOH) presented excellent recyclability. A potential catalytic mechanism for epoxide cycloaddition with CO2 into cyclic carbonate has been proposed.

Adsorption of small gas molecules onto boron nitride nanotubes and their Al-, Ga-, Cr- and Fe-doping derivatives for gas sensing, storage, and catalytic properties: Periodic DFT study

Based on the toxic gases and their conversion to non-toxic gases on the high potentials doping derivatives of boron nitride nanotubes (BNNTs), adsorption abilities of (5,5) and (10,0) BNNTs doped by selected dopants (Al, Ga, Cr and Fe) on small gas molecules was explored. Adsorption of small gas molecules, H2O, H2S, SO2, CO2, CO, NH3, N2O, and NO onto the pristine (5,5) and (10,0) BNNTs, their doping derivatives (Al-, Ga-, Cr- and Fe-doped (5,5) and (10,0) BNNTs) were investigated using periodic DFT method. Strong adsorptions of N2O (-4.26 eV) and SO2 (-2.56 eV) on the Cr-(5,5) and Cr-(10,0) BNNTs were found. Furthermore, the Cr-(5,5) and Cr-(10,0) BNNTs as the catalysts for N2O conversion to N2 and O2 were found. The Al- and Ga-(5,5) BNNTs, Al- and Ga-(10,0) BNNTs are suggested as the NO sensing materials and NH3 storage materials. All the suggested materials such Cr-(5,5), Cr-(10,0), Al-(5,5), Ga-(5,5), Al-(10,0) and Ga-(10,0) BNNTs could be experimentally tested for conversion, sensitivity, and storage of mentioned toxic gases in the future.

Ozone decomposition on transition-metal-atom anchored graphdiyne: Insights from computation and experiment

Transition-metal-atom anchored graphdiynes (TM@GDY, TM = Mn, Fe, Co, Ni and Cu) have already been synthesized and found applications in hydrogen evolution, nitrogen fixation and etc. By means of first-principle predictions and test experiments, we propose here that Fe@GDY and Co@GDY are efficient catalysts for the sustainable conversion of O3 to O2. These two catalysts can spontaneously chemisorb O3 with zero reaction barrier and have low O3 conversion barriers (0.31 eV and 0.19 eV, respectively). The O3 decomposition experiment in a continuous flow membrane reactor and electron paramagnetic resonance results verify that Fe@GDY and Co@GDY are efficient catalysts under humid conditions. Raman spectra prove the formation of the key Fe-O/Co-O and FeOO and CoOO intermediates. The hydrophobic nature of graphdiyne and the strongest chemisorption of O3 among tested ambient gases, make Fe@GDY and Co@GDY ideal catalysts under both dry and humid conditions. These findings would stimulate future explorations on metal anchored GDY-based catalysts for applications of toxic gas decomposition or fixation.

Surface exsolved NiFeOx nanocatalyst for enhanced alkaline oxygen evolution catalysis

A synergistically improved alkaline oxygen evolution catalyst of the NiFeOx nanoalloy oxide structure is introduced using an in-situ exsolution method. The separately doped Ni and Fe ions are exsolved on the surface of the perovskite as homogeneously distributed NiFeOx oxide alloy catalysts via following reduction and oxidation processes. The incorporation of additional Fe into the surface embedded NiFeOx catalyst improved the inherent oxygen evolution reaction (OER) property with fast reaction kinetics. Density functional theory (DFT) result indicates the lowest OER overpotential of NiFeOx catalyst is originated from the reduced energy barrier of surface *O formation from *OH group. The NiFeOx exsolved catalyst shows the smallest overpotential of 0.49 V (j = 10 mA∙cm−2) and Tafel slope (93 mV∙dec-1), compared with that of single NiO (0.54 V, 132 mV∙dec-1) and Fe3O4 catalyst. This study provides an effective method for developing nanosized OER catalysts for various energy conversion and storage electrode materials.

Facet and dual vacancy engineering-boosting BiOBr for enhanced CO2 and epoxide cycloaddition reaction under mild and cocatalyst-free conditions: Double substrate active sites and activated surface bromine ions synergy

Among the many strategies for CO2 resource utilization, the synthetic technology of cyclic carbonates with 100 % atom economy through CO2and epoxide is one of the most industrially viable routes, but its efficiency has been severely hampered by the lack of highly active catalytic sites. Moreover, due to the intrinsic thermodynamic stability and kinetic inertia of CO2 and the higher energy barrier of the ring-opening reaction of epoxides, the heterogeneous catalytic conversion of CO2 highly depends on harsh operating conditions, high temperatures and pressures, and the incorporation of cocatalysts. The development of efficient heterogeneous catalysts for CO2 conversion under cocatalyst-free and mild conditions has always been a challenge. Herein, we have proposed a synergetic strategy of facet and vacancy engineering for the construction of highly efficient heterogeneous catalyst BiO1-xBr1-y-(010) for CO2 cycloaddition, where introducing the OVs-BrVs pairs into typical (010) facets BiOBr with simultaneous surface Lewis acid sites Bi3+ and nucleophilic sites Br−. By combining theoretical calculations and a series of systematic experiments, such as CO2 temperature-programmed desorption, electron paramagnetic resonance and fluorescence probe analysis experiments, the introduced OVs-BrVs pair can not only form Bi3+-Bi(3-x)+ dual active sites on the surface, which activate PO and CO2 respectively to reduce the energy barrier of CO2 insertion, but also activate Br− near BrVs to enhance their nucleophilic attacking ability and reduce the energy barrier of epoxides ring-opening. As a result, the BiO1-xBr1-y-(010) with abundant surface OVs-BrVs pairs showed a high cyclic carbonates conversion of 99 % with 100 % selectivity under cocatalyst-free and mild conditions, far surpassing most heterogeneous catalytic systems. This work provides a completely new strategy to construct high-performance heterogeneous CO2 cycloaddition catalysts through a simple facet and vacancy engineering strategy to overcome the harsh operating conditions limitation and the use of cocatalysts.

Biodiesel Production via Transesterification Reaction over Mono- and Bimetallic Copper-Noble Metal (Pt, Ru) Catalysts Supported on BEA Zeolite

This work focuses on the study of biodiesel production from commercial rapeseed oil and methanol via transesterification reactions on monometallic copper and bimetallic copper–noble metal (platinum, ruthenium) catalysts supported on BEA zeolite. The catalysts were prepared by wet impregnation method on the hydrogen form of BEA zeolite. As part of the study, the physicochemical and catalytic properties of the prepared catalytic materials were determined. The catalytic activity tests were carried out in the transesterification reaction over prepared catalysts at 220 °C for 2 h in an autoclave. The physicochemical properties of the obtained catalysts were investigated by X-ray diffraction (XRD), specific surface area and porosity (BET), a scanning electron microscope equipped with an energy dispersive spectrometer (SEM–EDS) and temperature-programmed desorption of ammonia (TPD-NH3) method. The results of the catalytic activity showed the promotional effect of the noble metal on the TG conversion and FAME efficiency of copper catalysts in the biodiesel production process. The most active catalyst turned out to be the calcined 5%Cu–1%Ru/BEA catalyst, which showed the highest TG conversion of 85.7% and the second highest FAME efficiency of 58.4%. The high activity of this system is explained by its surface acidity and large specific surface area.

Electron Structure Tuned Oxygen Vacancy-Rich AuPd/CeO2 for Enhancing 5-Hydroxymethylfurfural Oxidation.

The design of high activity catalyst for the efficiently conversion of 5-hydroxymethylfurfural (HMF) to 2,5-furandicarboxylic acid (FDCA) gains great interest. The rationally tailoring of electronic structure directly affects the interaction between catalysts and organic substrates, especially molecular oxygen as the oxidant. This work, the bimetallic catalysts AuPd/CeO2 were prepared by the combining method of chemical reduction and photo-deposition, effectively concerting charge between Au and Pd and forming the electron-rich state of Au. The increasing of oxygen vacancy concentration of CeO2 by acidic treatment can facilitate the adsorption of HMF for catalysts and enhance the yield of FDCA (99.0 %). Moreover, a series of experiment results combining with density functional theory calculation illustrated that the oxidation performance of catalyst in HMF conversion was strongly related to the electronic state of interfacial Au-Pd-CeO2. Furthermore, the electron-rich state sites strengthen the adsorption and activation of molecular oxygen, greatly promoting the elimination of β-hydride for the selective oxidation of 5-hydroxymethyl-2-furancarboxylic acid (HMFCA) to FDCA, accompanied with an outgoing FDCA formation rate of 13.21 mmol ⋅ g-1 ⋅ min-1 at 80 °C. The perception exhibited in this research could be benefit to understanding the effects of electronic state for interfacial sites and designing excellent catalysts for the oxidation of HMF.

Controlled Synthesis of Graphdiyne-Based Multiscale Catalysts for Energy Conversion

Controlled Synthesis of Graphdiyne-Based Multiscale Catalysts for Energy Conversion

Tunable products of 5-hydroxymethylfurfural oxidation by Zn/Co-ZIF derived catalysts

As a bio-based platform compound, 5-hydroxymethylfurfural (HMF) can be effectively converted into other high value-added derivatives. Here we report two non-noble metal catalysts for the selective oxidation of HMF, NC and Co@NC are easily obtained by pyrolysis of ZIF-8 and ZIF-67, respectively. The NC and Co@NC catalysts oxidized HMF to FFCA (Select. 95 %) and FDCA (Select. 98 %), respectively, using O2 as oxidant. Experimental and theoretical studies show that pyridinic N and graphitic N in NC has high catalytic activity for the oxidation of carbonyl groups in HMF to FFCA, while the synergistic effect of Co-N in Co@NC can completely oxidize HMF to FDCA. DFT calculations show that, compared with NC, the Co@NC containing Co-N exhibits a lower energy barrier during the aerobic oxidation of HMF to FDCA. And Co-N leads to the conversion of electrons from N to Co and promotes the activation of O2 to form O2-, and then oxidize HMF to FDCA. Interestingly, our reaction system is universal, and could achieve almost 100 % conversion of various furfural substrates to corresponding carboxylic acid. This study may provide a new/highly efficient catalysts for biomass conversion.

Dry reforming of ethane over titania-based catalysts for higher selectivity and conversion to syngas

Ethane, one of the key components of shale gas, is a valuable feedstock for the production of syngas (CO + H2) via the CC bond cleavage during dry reforming of ethane (DRE) reaction. Selective catalysts are needed to direct this reaction pathway against the competing CH bond cleavage for ethylene formation. In this study, Fe, V and Rh oxides supported on TiO2 catalysts were prepared by impregnation method. The catalysts were tested for DRE with the main target of enhancing selectivity to syngas (CO and H2) and reducing byproducts (methane and ethylene) formation. The catalysts were characterized using X-ray diffraction, scanning electron microscopy, NH3/CO2 temperature programmed desorption and H2-temperature programmed reduction. Temperature programmed oxidation was utilized to characterize the coke contents of the spent catalysts. The catalysts were evaluated for DRE reaction in a fixed-bed reactor at the temperature range from 500 °C to 650 °C and CO2/ethane ratio from 2.0 to 10.0 (mol/mol). It was found that ethane conversion over the three catalysts increased in the order Rh/TiO2 > Fe/TiO2 > V/TiO2. Rh/TiO2 catalyst exhibited > 99 % ethane conversion, 36 % and 61 % yields of H2 and CO, respectively, at 650 °C and CO2/ethane ratio of 5.0. The high conversion of ethane was mainly attributed to the enhanced dispersion of Rh oxides on the TiO2 support coupled with the balanced surface acidic and basic sites. The Rh catalyst facilitated CC bond dissociation of ethane thereby forming methyl intermediates which then reacted with adsorbed CO2, thereby enhancing syngas production during DRE reaction.

Catalytic fast pyrolysis over heavy metals-containing livestock manure biochar catalyst for polystyrene upcycling

The perpetual market demand for polystyrene results in the gradual accumulation of polystyrene waste, placing a serious burden on the environment. This study proposed a promising method to upcycle polystyrene for styrene-derived monomers through catalytic fast pyrolysis. The metals-incorporated biochar catalysts were synthesized from heavy metals-contaminated manure waste for catalytic fast pyrolysis of polystyrene. The experimental results showed that the bimetallic biochar-derived catalyst containing Zn and Cr (Zn-Cr/C) was more conducive to the liquid production, with an extremely high yield of 88.22 wt%. Monometallic Pb-incorporated biochar catalyst (Pb/C) and bimetallic Zn-Cu co-doped on biochar (Zn-Cu/C) were more favorable for the production of pure styrene, with the mass yield of 61.26 wt% and 60.39 wt%, respectively. Additionally, the study elucidated a deep understanding of the reaction mechanisms involved in the catalytic fast pyrolysis of polystyrene. Simply put, this study introduced a new concept to convert heavy metal-contaminated animal manure into metal-incorporated biochar catalysts for catalytic conversion of polystyrene waste in pure styrene-based monomers.

Magnetic biochar catalyst from reed straw and electric furnace dust for biodiesel production and life cycle assessment

A novel magnetic carbon-based catalyst was prepared from solid waste (reed straw and electric furnace dust) by coprecipitation and high temperature pyrolysis with excellent application potential. Single factor and response surface experiments were used to optimise the catalyst preparation process (mass ratio of reed straw/electric furnace dust of 5:1 at 500 °C in 4 h) and biodiesel production, respectively, with results of 99.89 wt% biodiesel yield in the first cycle (93.61 wt% after 11 cycles) obtained at 74.15 oC in 4.16 h with a 14.06:1 molar ratio of methanol/oil and 7.75 wt% catalyst. The life cycle assessment of magnetic carbon-based catalysts for biodiesel production suggested that the soybean oil extraction stage had the greatest impact on the environment, mainly from the use of soybeans and electricity. Solid waste as raw material to prepare catalysts for biomass energy conversion was proven to be a good strategy for energy conservation and emission reduction. This study provides guidance sustainable biomass energy conversion with low cost, low energy consumption, and minimal negative environmental impact.

Regulating the oxygen vacancy of M-WOx-MgOy catalysts (M = Ni, Pd, Pt, Ru) for the chemoselective conversion of glucose to diols

A series of M-WOx-MgOy (M = Ni, Pd, Pt, Ru) catalysts was prepared and their catalytic performances were systematically investigated in the chemoselective hydrogenolysis of glucose to diols. Among these catalysts, Ru-WOx-MgOy exhibited superior catalytic activity in the production of diols as well as ethylene glycol from glucose under mild reaction conditions. Then various Characteristic techniques including XRD, BET, FTIR, SEM, TEM, HAADF-STEM, XPS, NH3-TPD, and Pyridine-adsorbed DRIFTS were adopted to investigate the structural properties of these catalysts and correlate them with their catalytic performances. Based on these characterization results, it showed that the outstanding catalytic activity of Ru-WOx-MgOy catalyst was attributed to its higher content of oxygen vacancies, which served as the active acidic sites and greatly lowered the activation energy required for glucose conversion, thereby promoting the efficient production of diols.

One-pot catalytic conversion of sugars to methyl lactate over acid-base bifunctional Sn/MgO catalysts

Alkyl lactates represent such green added-value chemicals that commonly used as biodegradable green solvents, detergents, pharmaceutical intermediates et al. Catalytic conversion of carbohydrates to methyl lactate (MLA) is a representative way for high-value utilization of biomass and the key lies in the development of highly efficient catalysts. In methanol, strong acid or alkaline catalysts are usually used under high temperature and high pressure, suffering from problems such as low selectivity, high cost or contamination of environment. This study aims to develop an acid-base bifunctional heterogeneous catalyst for the one-pot conversion of sugars to MLA under mild conditions. Sn/Mg composite oxides was synthesized by a coprecipitation method and further modified by poly (vinyl imidazole) ([PVIM]) to tune the hydrophilicity. Effect of polymer and Sn amount, calcination temperature, reaction temperature, catalyst dosage, and substrate concentration were investigated. The acid-base properties were characterized by NH3-TPD, pyridine-FTIR and CO2-TPD analysis. It was found that the presence of medium acid sites and medium base sites played an important role to the cascade reactions of carbohydrates to MLA. An optimum MLA yield of 55.4% was achieved over 10[PVIM]-5Sn/MgO (0.05g) with complete conversion of glucose (28mM) at 140 ℃, 2MPa N2 for 10h. The reaction conditions are mild and no strong acid or strong base catalyst is required. Furthermore, a possible reaction mechanism was proposed that the introduction of [PVIM] effectively regulated the local microenvironment of active sites and the acid base synergism greatly promoted the retro-aldol condensation, dehydration and hydrogen transfer reactions during the conversion of glucose to MLA.

Hierarchical Hollow TiO2@Bi2WO6 with Light-Driven Excited Bi(3-x)+ Sites for Efficient Photothermal Catalytic CO2 Reduction.

Converting CO2 into valuable chemicals via sustainable energy sources is indispensable for human development. Photothermal catalysis combines the high selectivity of photocatalysis and the high yield of thermal catalysis, which is promising for CO2 reduction. However, the present photothermal catalysts suffer from low activity due to their poor light absorption ability and fast recombination of photogenerated electrons and holes. Here, a TiO2@Bi2WO6 heterojunction photocatalyst featuring a hierarchical hollow structure was prepared by an in situ growth method. The visible light absorption and photothermal effect of the TiO2@Bi2WO6 photocatalyst is promoted by a hierarchical hollow structure, while the recombination phenomenon is significantly mitigated due to the construction of the heterojunction interface and the existence of excited Bi(3-x)+ sites. Such a catalyst exhibits excellent photothermal performance with a CO yield of 43.7 μmol h-1 g-1, which is 15 and 4.7 times higher than that of pure Bi2WO6 and that of physically mixed TiO2/Bi2WO6, respectively. An in situ study shows that the pathway for the transformation of CO2 into CO over our TiO2@Bi2WO6 proceeds via two important intermediates, including COO- and COOH-. Our work provides a new idea of excited states for the design and synthesis of highly efficient photothermal catalysts for CO2 conversion.

Ni supported on Ti-doped SBA-15 catalyst for the selective hydrodeoxygenation conversion of lignin derivatives

The development of cost-effective and efficient catalysts plays a critical role in the selective hydrodeoxygenation of lignin derivatives for lignin valorization. Herein, we reported “metal-acid” bifunctional catalysts (Ni/Ti-SBA-15) consist of Ni nanoparticles highly dispersed on Ti doped SBA-15, which achieved 100% vanillin conversion and 96.46% selectivity of 2-methoxy-4-methylphenol (MMP) under mild conditions. Characterizations were employed to reveal the morphology and physicochemical properties of the catalysts. The results indicated that doping of Ti species not only increased the number of acidic sites but also promoted the high dispersion of Ni nanoparticles on the support. This research provides a novel concept for the synthesis of cost-effective and efficient catalysts, which contributes to the environmentally friendly and economical conversion of biomass derivatives.

A Unique Amorphous Porous BiSbOx Nanotube with Abundant Unsaturated Sb‐Stabilized BiO8−x Sites for Efficient CO2 Electroreduction in a Wide Potential Window

AbstractThe CO2 electroreduction reaction using sustainable electricity emerges as a viable strategy to produce high‐value‐added and profitable chemicals. The achievement of superior activity at a lower overpotential and higher selectivity in a wide potential window is vitally important for large‐scale industrial applications. Herein, a carbon‐composite amorphous porous BiSbOx nanotube with abundant unsaturated sites is reported to boost the conversion of CO2 to formate, exhibiting a formate selectivity of >90% in an extremely broad range of potentials from −0.5 to −1.4 V versus reversible hydrogen electrode (RHE) and a maximal energy conversion efficiency of 77.1%. Importantly, pure formic acid solution is directly obtained in a solid‐electrolyte cell for industrial‐scale applications. The porous tubular structure can expose more catalytic active sites, accelerate the mass transfer, and show fast surface charge transfer. Moreover, the unique coordination‐unsaturated Sb‐stabilized BiO8−x site can not only enhance the adsorption and activation of CO2 but also reasonably balance the stabilization and hydrogenation of *OCHO intermediate, thus leading to its obviously higher catalytic performance. As a result, a novel amorphous porous BiSbOx nanotube is successfully designed for efficient CO2 electroreduction, which may shed new light on developing many more amorphous composite metal oxide catalysts for conversion of inert small molecules.