Mass Transfer Limitations Research Articles

Temperature-Dependent Selectivity and Detection of Hidden Carbon Deposition in Methane Oxidation.

Reaction products in heterogeneous catalysis can be detected either on the catalyst surface or in the gas phase after desorption. However, if atoms are dissolved in the catalyst bulk, then reaction channels can become hidden. This is the case if the dissolution rate of the deposits is faster than their formation rate. This might lead to the underestimation or even overlooking of reaction channels such as, e.g., carbon deposition during hydrocarbon oxidation reactions, which is problematic as carbon can have a significant influence on the catalytic activity. Here, we demonstrate how such hidden deposition channels can be uncovered by carefully measuring the product formation rates in the local gas phase just above the catalyst surface with time-resolved ambient pressure X-ray photoelectron spectroscopy. As a case study, we investigate methane oxidation on a polycrystalline Pd catalyst in an oxygen-lean environment at a few millibar pressure. By ramping the temperature between 350 and 525 °C, we follow the time evolution of the different reaction pathways. Only in the oxygen mass-transfer limit do we observe CO production, while our data suggests that carbon deposition also happens outside this limit.

Modeling mass transfer limitations driven by electrowetting in electrochemical CO2 reduction at silver gas diffusion electrodes

A one-dimensional mathematical model of a silver gas diffusion electrode (GDE) in electrochemical CO2 reduction (eCO2R) is presented. A Leverett approach is utilized to describe the coexistence of gaseous and liquid phases in the porous GDE, accounting for the potential-dependent contact angle of silver influenced by electrowetting. The model is fit to a set of experimental steady state results for sprayed electrodes with a range of diluted feeds (25−100vol%CO2). The model results ascertain a high electrolyte saturation in the GDE as the main cause for the inherent mass transfer limitations during eCO2R at elevated current densities. Furthermore, precipitation as a result of increased local K2CO3 concentration that surpasses the solubility limit is determined as degradation mechanism at current densities >3kAm−2. It is demonstrated how the model can be used to examine the effects of design parameters, indicating benefits of more hydrophobic and thinner GDEs.

Highly-efficient hydrogen production through the electrification of OB-SiC nickel structured catalyst: Methane steam reforming and ammonia cracking as case studies

The aim of this work is the preparation and the electrification of Ni_CeO2_Al2O3/OBSiC (Oxygen Bonded SIlicon Carbide) based foams used in two different endothermic reactions for H2 production: methane steam reforming and ammonia cracking. In particular, the heating of the catalytic foams occurs by the Joule effect, and to guarantee a uniform temperature profile in both the axial and radial direction, two different heating resistances were used. In addition, the high tortuosity together with the very high thermal conductivity of the OBSIC carrier, allow to overcome the heat and mass transfer limitations achieving a better control of the reaction behavior.Wet impregnation method was adopted for the Ni and Ce deposition, while the final catalysts was characterized through Hg penetration technique, Scanning Electron Microscope (SEM), N2 adsorption @77 K for the specific surface areas (SSA) determination and X-ray diffraction (XRD). The methane steam reforming and ammonia cracking tests were both carried out, in the same reactor, but at different space velocity values (WHSV). The results obtained are exciting, not only in terms of equilibrium approach and hydrogen production, but also in terms of energy consumption as kWh/Nm3 of H2 produced. In particular, in the case of methane steam reforming the results showed an energy consumption E [kWh/Nm3 H2] equal to 1.21 obtained at WHSV equal to 6.2 h−1, very close to the theoretical limit of 0.98 kW h/Nm3 H2. Also, for ammonia cracking, the energy consumption was very promising considering the scale of our reactor, with 1.5 kW h/Nm3 H2 obtained at a WHSV of 2.27 h−1, considering the theoretical limit equal to 0.71 kW h/Nm3 H2.

Behavior of enzymatic membranes under pressure: Effect of enzyme location

Enzyme immobilized membranes combine catalysis and separation functions. Their application in large-scale continuous processes requires knowing the behavior under pressure. Also, the effects of enzyme location on the mass transfer limitation, membranes’ stability, and filtration performance should be investigated. In this study, urease (URE) and trypsin (TRY) enzymes were physically immobilized in/on the surface of a polyacrylonitrile (AN69) membrane through layer-by-layer (LbL) self-assembly method using polyethylenemine (PEI) and sodium-alginate (ALG) as cationic and anionic polyelectrolytes respectively. URE, located on the membrane’s surface, degraded urea in a reaction-controlled regime, and its immobilization did not significantly change the hydraulic permeability. On the other hand, the TRY enzyme attached to the membrane’s pores reduced the permeability and degraded the BAPNA in a diffusion-controlled region. In TRY immobilized membranes, the conversion increased linearly with the transmembrane pressure, while in URE immobilized ones, conversion was maximum at 1 bar. Sandwiching the enzymes between two polyelectrolytes resulted in the highest catalytic activities. This configuration maintained most of the URE activity in the long-term filtration, but it did not help prevent TRY’s activity loss.

Modeling of Mass Transfer and Reaction Kinetics in ZnO Nanoparticle Micro-Reactor Systems for AMX and DOX Degradation

This study aims to model the coupled phenomena of photocatalytic reaction and mass transfer in the degradation of Amoxicillin (AMX) and Doxycycline (DOX) using Zinc oxide (ZnO) nanoparticles within microreactor systems. The objective is to gain a comprehensive understanding of the dynamic interaction between the photocatalytic degradation kinetics and the mass transfer processes to optimize the conditions for efficient antibiotic removal from contaminated water. This involves characterizing the reaction kinetics via the Langmuir-Hinshelwood model, estimating the mass transfer coefficients, and analyzing the effects of axial dispersion to ensure the accurate determination of intrinsic kinetic constants and minimize mass transfer limitations. This study used a syringe pump to ensure a consistent flow of antibiotic solution into the microreactor. The results indicate that AMX reaches adsorption equilibrium more rapidly than DOX, corresponding to its faster photocatalytic degradation kinetics and higher final conversion rate (89% for AMX, 86% for DOX). The mass transfer coefficient (kd) was estimated using the Sherwood number, derived from three different models, with the constant Sherwood model best fitting the R1 microreactor data. An analysis of the Damköhler number (DaII) indicates that high flow rates minimize mass transfer limitations in the R1 microreactor, allowing the determination of near-intrinsic kinetic constants. On the contrary, at low flow rates, kinetic constants are apparent as a result of mass-transfer limitations. The study concludes that higher flow rates (≥ 10 mL/h) in the R1 microreactor are preferable to approach intrinsic kinetics and reduce mass transfer limitations during photocatalytic degradation of antibiotics. These findings underscore the potential of ZnO-based oxidation processes in treating antibiotic-contaminated water with optimized conditions, providing a pathway for efficient and sustainable wastewater treatment.

Efficient synthesis of γ-valerolactone from ethyl levulinate via catalytic transfer hydrogenation in supercritical isopropanol over nickel aluminum oxide nanosheets

This study reports a novel method for γ-valerolactone (GVL) production from ethyl levulinate (EL) utilizing non-noble metal catalysts within a supercritical isopropanol (IPA) system. Nickel-loaded nickel–aluminum oxide nanosheets (NiXAl-R) were fabricated via hydrothermal treatment of Ni–Al layered double hydroxide precursors, followed by hydrogen reduction at 550 °C for 1.5 h. Using NiXAl-R as the catalyst and IPA as the hydrogen donor, we achieved notable results: 82.7% EL conversion, 73.6% GVL yield, and 1.178 molGVL g−1 h−1 reaction efficiency after 1.5 h in supercritical IPA. The catalytic activity of NiXAl-R remained stable over five catalytic cycles. The surface of NiXAl-R exhibits abundant oxygen vacancies and unsaturated Al species (Alx+), which promote the initial transfer hydrogenation of EL to form the ethyl 4-hydroxypentanoate (4-HPE) intermediate. Simultaneously, the supercritical IPA environment overcomes mass transfer limitations at the solid–liquid interface between 4-HPE and the catalyst, thereby facilitating the Alx+-catalyzed intramolecular esterification of 4-HPE into GVL.

Carbon Support Enhanced Mass Transfer and Metal-Support Interaction Promoted Activation for Low-Concentrated Nitric Oxide Electroreduction to Ammonia.

The electrochemical NO reduction reaction (NORR) is a promising approach for both nitrogen cycle regulation and ammonia synthesis. Due to the relatively low concentration of the NO source and poor solubility of NO in solution, mass transfer limitation is a serious but easily overlooked issue. In this work, porous carbon-supported ultrafine Cu clusters grown on Cu nanowire arrays (defined as Cu@Cu/C NWAs) are prepared for low-concentration NORR. A high Faradaic efficiency (93.0%) and yield rate (1180.5 μg h-1 cm-2) of ammonia are realized on Cu@Cu/C NWAs at -0.1 V vs a reversible hydrogen electrode (RHE), which are far superior to those of Cu NWAs and other reported performances under similar conditions. The construction of a porous carbon support can effectively decrease the NO diffusion kinetics and promote NO coverage for subsequent highly effective conversion. Moreover, the favorable metal-support interaction between ultrafine Cu clusters and carbon support enhances the adsorption of NO and decreases the barrier for *HNO formation in comparison with that of pure Cu NWAs. Overall, the whole NORR can be fully strengthened on Cu@Cu/C NWAs at low NO concentrations.

Spatial Confinement of Co Nanoparticles in N-Doped Carbon Nanorods for Wastewater Purification via CaSO3 Activation.

Spatial confinement of organic pollutants and reactive oxygen species (e.g., SO4•- and •OH) with ultrashort lifetime inside the scale of chemical theoretical diffusion could provide a greatly promising strategy to overcome the limitation of mass transfer in the heterogeneous Fenton-like oxidation process. Herein, we first reported spatial confinement of cobalt nanoparticles in N-doped carbon nanorods (Co-NCNRs), by encapsulating Co nanoparticles into N-doped carbon nanorods, in activating CaSO3 for antibiotic degradation. Compared to Na2SO3 and NaHSO3, CaSO3 could slowly and persistently discharge SO32- due to its low solubility, thus avoiding the depletion of the generated SO3•- and •OH under the high concentration of sulfite ions. Fully physical characterizations confirmed that the 3D hydrogel was mostly transformed into the nanorod structure of Co-NCNRs at 550 °C. Co atoms were successfully nanoconfined into N-doped carbon nanorods, which contributes to mass transfer and prevents the agglomeration of Co nanoparticles, thus enhancing its catalytic activity and stability in activating CaSO3 for water decontamination. The catalytic performance, kinetic research, influences of inorganic anions, pH, and degradation mechanism of chlortetracycline degradation catalyzed by the Co-NCNRs/CaSO3 system have been studied in detail. This work not only proposed a facile method for synthesis of nanoconfined catalyst but also provided an excellent Co-NCNRs/CaSO3 system for wastewater treatment.

Electrochemical reclamation of oil sands process water: Two and three-dimensional electrode configuration systems structured with different anode materials

Several studies have indicated the potential of the electrochemical advanced oxidation process in oil sands process water (OSPW) reclamation; however, the variations in different electrode configuration systems and anode materials remain elusive. This study assembled a two-dimensional electrode system (2-DES) and a packed bed electrode reactor (PBER) for OSPW reclamation, of which boron-doped diamond (BDD) (non-active anode), dimensionally stable anodes (DSA-RuO2 and DSA-IrO2) and graphite (active anodes) were selected as the anode materials, while in PBER, spherical activated carbon (SAC) was added as the third electrode. Within the 2-DES, BDD achieved over 60% removal of chemical oxygen demand (COD) due to its excellent •OH generation ability, while DSAs generated the most active chlorine and were quickly consumed by organic matter during the first 30 minutes. However, mass transfer limitation restricted the 2-DES treatment efficiency regardless of the anode materials employed, particularly resulting in limited removal of naphthenic acids (NAs). Compared to 2-DES, PBER significantly improved the OSPW treatment under identical electrolysis conditions, achieving over 91% COD and 99% NAs removal using DSA-IrO2 + SAC. Because of the contribution of the third electrode in PBER, the performance differences between various anode materials were less substantial than in the case of 2-DES. Packed SAC enhanced the mass transfer performance and generation of radical oxidants during OSPW electrolysis, improving the OSPW electrochemical treatment process. Additionally, SAC adsorbed most free chlorine from the liquid phase, avoiding the formation of halogenated organic compounds in reclaimed OSPW.

Pore-scale visualization of hydrate dissociation and mass transfer during depressurization using microfluidic experiments

Natural gas hydrate is a potential low-carbon energy resource. Extracting this resource efficiently remains a challenge, due to the intricacies involved in multiphase reactive transport during hydrate dissociation. This study employs microfluidic experimental techniques to observe pore-scale interactions during depressurization-induced hydrate dissociation, utilizing high-resolution spatial and temporal imagery. Supervised machine learning algorithms segmented these microscopic images, enabling the analysis of phase saturation changes and hydrate dissociation rates. The study identifies two distinct hydrate forms in microfluidic chips: hydrate films and crystals, each exhibiting unique dissociation characteristics. Hydrate films decomposed rapidly in response to pressure reductions below equilibrium with the dissociation rate of O(10−1 %/s) under stationary gas–water conditions. When considering gas–water migration, the gas encapsulated in the hydrate film will be displaced by water, leading to a reduced dissociation rate. The hydrate crystal dissociation is much slower with the dissociation rate of O(10−3 %/s) under stationary gas–water conditions compared to the hydrate film, hindered by mass transfer limitations. Gas-water migration can enhance crystal dissociation. The formation and expansion of gas microbubbles under depressurization accelerated hydrate dissociation within a confined temporal and spatial range, which was known as the self-promotion mechanisms. Significantly, depressurization-induced gas slug flow increases the dissociation rate by more than one order of magnitude, compared to that in stationary gas–water conditions. The depressurization process played a significant role, not only by facilitating thermodynamic feasibility for hydrate dissociation but also by inducing the critical gas slug flow. These results of the present study provide theoretical guidance for improving natural gas hydrate production efficiency.

One-pot synthesis and biochemical characterization of the novel magnetic phospholipase D nanoflowers modified with polyphenols

Phospholipase D (PLD) can catalyze the hydrolytic cleavage of phosphodiester bonds and transphosphatidylation and has been widely employed in the chemical and pharmaceutical fields. To improve the stability and reusability of PLD, an immobilized enzyme system was developed using magnetic nanoparticles modified with polyphenols (dopamine and tannic acid) and metal hybrid nanoflowers to co-immobilize phospholipase D (PLD). This immobilization technique aimed to improve the enzymatic performance through increased surface area, reduced mass transfer limitations, and facilitated reuse. The hydrolytic and transphosphatidylation activities of PLD immobilized on polyphenol-modified magnetic nanoflowers (PDA-MNFs and TA-MNFs) were evaluated and compared to free PLD. PDA-MNFs and TA-MNFs showed significantly enhanced hydrolytic activity (19.9-fold and 21.7-fold increases, respectively) and transphosphatidylation activity (over 1.79-fold and 1.96-fold increases, respectively) compared to free PLD. Temperature and pH stability were also markedly improved for the immobilized PLD. After 10 reuse cycles, PDA-MNFs and TA-MNFs retained over 65 % of their initial transphosphatidylation activity. Therefore, this co-deposition and polymerization immobilization strategy using polyphenol-modified magnetic nanoflowers has the potential for efficiently increasing enzymatic performance and synthesizing industrially relevant compounds like phosphatidic acid and phosphatidylserine

Bubble Turbulent Gas-Permeable Membrane for Ammonia Recovery from Swine Wastewater: Mass Transfer Enhancement and Antifouling Mechanisms.

Recovering ammonium from swine wastewater employing a gas-permeable membrane (GM) has potential but suffers from the limitations of unattractive mass transfer and poor-tolerance antifouling properties. Turbulence is an effective approach to enhancing the release of volatile ammonia from wastewater while relying on interfacial disturbance to interfere with contaminant adhesion. Herein, we design an innovative gas-permeable membrane coupled with bubble turbulence (BT-GM) that enhances mass transfer while mitigating membrane fouling. Bubbles act as turbulence carriers to accelerate the release and migration of ammonia from the liquid phase, increasing the ammonia concentration gradient at the membrane-liquid interface. In comparison, the ammonium mass transfer rate of the BT-GM process applied to real swine wastewater is 38% higher than that of conventional GM (12 h). Through a computational fluid dynamics simulation, the turbulence kinetic energy of BT-GM system is 3 orders of magnitude higher than that of GM, and the effective mass transfer area is nearly 3 times that of GM. Seven batches of tests confirmed that the BT-GM system exhibits remarkable antifouling ability, broadens its adaptability to complex water quality, and practically promotes the development of sustainable resource recycling.

Aromatic Ethers Induced Electronic Structure Reconstruction on Encapsulated Nickel Catalysts for High-Performance Catalytic Hydrogenation.

Carbon-encapsulated metal (CEM) catalysts effectively address supported metal catalyst instability by protecting the active metal with a shell. However, mass transfer limitations lead to reduced activity for catalytic hydrogenation reaction over most CEM catalysts. Herein, we introduce a dopant strategy aimed at incorporating nickel metal within graphene-like shells (GLS) featuring oxygen-containing functional groups (OFGs). The core of this strategy involves precise control of GLS modification and the demonstrated pivotal influence of aromatic ether linkages (═C-O-C) in GLS for significant enhancement of catalytic performance. The introduction of ═C-O-C into GLS with stability was beneficial to improve the work function of the catalyst and promoted electron transmission from Ni metal core to GLS, further elevating the catalytic activity, based on the Mott-Schottky effect. In addition, the experimental characterization and density functional theory (DFT) calculations showcased that the ═C-O-C reconstructed the electronic state of GLS, imparting it highly specific for the adsorption of hydrogen and para-chloronitrobenzene (p-CNB) to obtain para-chloroaniline (p-CAN) with high selectivity. This work manifested a feasible direction for the precise modulation and design of the OFGs in CEM catalysts to achieve highly efficient catalytic hydrogenation.

Universal growth of perovskite thin monocrystals from high solute flux for sensitive self-driven X-ray detection

Metal-halide perovskite thin monocrystals featuring efficient carrier collection and transport capabilities are well suited for radiation detectors, yet their growth in a generic, well-controlled manner remains challenging. Here, we reveal that mass transfer is one major limiting factor during solution growth of perovskite thin monocrystals. A general approach is developed to overcome synthetic limitation by using a high solute flux system, in which mass diffusion coefficient is improved from 1.7×10–10 to 5.4×10–10 m2 s–1 by suppressing monomer aggregation. The generality of this approach is validated by the synthesis of 29 types of perovskite thin monocrystals at 40–90 °C with the growth velocity up to 27.2 μm min–1. The as-grown perovskite monocrystals deliver a high X-ray sensitivity of 1.74×105 µC Gy−1 cm−2 without applied bias. The findings regarding limited mass transfer and high-flux crystallization are crucial towards advancing the preparation and application of perovskite thin monocrystals.

Insights into the Mechanism of Selective Removal of Heavy Metal Ions by the Pulsed/Direct Current Electrochemical Method.

Heavy metal pollution treatment in industrial wastewater is crucial for protecting biological and environmental safety. However, the highly efficient and selective removal of heavy metal ions from multiple cations in wastewater is a significant challenge. This work proposed a pulse electrochemical method with a low-/high-voltage periodic appearance to selectively recover heavy metal ions from complex wastewater. It exhibited a higher recovery efficiency for heavy metal ions (100% for Pb2+ and Cd2+, >98% for Mn2+) than other alkali and alkaline earth metal ions (Na+, Ca2+, and Mg2+ were kept below 3.6, 1.3, and 2.6%, respectively) in the multicomponent solution. The energy consumption was only 34-77% of that of the direct current electrodeposition method. The results of characterization and experiment unveil the mechanism that the low-/high-voltage periodic appearance can significantly suppress the water-splitting reaction and break the mass-transfer limitation between heavy metal ions and electrodes. In addition, the plant study demonstrates the feasibility of treated wastewater for agricultural use, further proving the high sustainability of the method. Therefore, it provides new insights into the selective recovery of heavy metals from industrial wastewater.

Production of biodiesel from waste fish fat through ultrasound-assisted transesterification using petro-diesel as cosolvent and optimization of process parameters using response surface methodology

Biodiesel is a highly promising and viable alternative to fossil-based diesel that also addresses the urgent need for effective waste management. It can be synthesized by the chemical modification of triglycerides sourced from vegetable origin, animal fat, or algal oil. The transesterification reaction is the preferred method of producing biodiesel. However, the non-miscibility of alcohol and oil layer causes excessive utilization of alcohol, catalyst, and a substantial reacting time and temperature. In the current investigation, transesterification of waste fish oil was performed with petro-diesel as cosolvent, under the influence of ultrasound energy. The combination of both techniques is a unique and efficient way to minimize the mass transfer limitations considerably and hence reduces the parameters of the reaction. It is also a sincere effort to comply with the principles of green chemistry. The optimum reaction conditions were obtained using response surface methodology (RSM) that were as follows: molar ratio of methanol to oil 9.09:1, catalyst concentration of 0.97 wt%, cosolvent concentration of 29.1 wt%, temperature 60.1℃, and a reacting time 30 min. Under these listed conditions, 98.1% biodiesel was achievable, which was in close agreement with the expected result. In addition, the cosolvent removal step from the crude biodiesel was also eliminated as it could be employed as a blended fuel in CI engines.

Direct electrochemical evidence suggests that aqueous microdroplets spontaneously produce hydrogen peroxide

Recent reports have detailed the striking observation that electroactive molecules, such as hydrogen peroxide (H2O2) and radical water species (H2O.+/H2O.-), are spontaneously produced in aqueous microdroplets. Stochastic electrochemistry allows one to study reactions in real-time occurring inside subfemtoliter droplets, one droplet at a time, when a microdroplet irreversibly adsorbs to an ultramicroelectrode surface (radius ~ 5 µm). Here, we use stochastic electrochemistry to probe the formation of hydrogen peroxide (H2O2) in single aqueous microdroplets suspended in 1,2-dichloroethane. The oxidation of H2O2 at alkaline pH (11.5) differs from near-neutral conditions (6.4), allowing us to create a digital, turn-off sensing modality for the presence of H2O2. Further, we show that the stochastic electrochemical signal is highest at the mass transfer limitation of the H2O2 couple and is dampened when the potential nears the formal potential. We validate these results by showing that the addition of a H2O2 selective probe, luminol, decreases the stochastic electrochemical response at alkaline pH (11.5). Our results support the observation that H2O2 is generated in water microdroplets at concentrations of ~100 s of µM.

Structural design and particle size examination on NiO-CeO2 catalysts supported on 3D-printed carbon monoliths for CO2 methanation

3D-printed high-surface carbon monoliths have been fabricated and tested as catalyst supports of CO2 methanation active phases (NiO-CeO2, 12 wt% Ni). The carbon carriers show a developed microporosity and good adherence to the catalytic phases of NiO-CeO2, showing great stability and cyclability. Two monolith designs were used: a conventional parallel-channeled structure (honeycomb) and a complex 3D network of non-linear channels built upon interconnected circular sections (circles), where flow turbulences along the reactant gas path are spurred. The effect of the active phases particle size on the catalyst distribution and the overall performance has been assessed by comparing NiO-CeO2 nanoparticles of 7 nm average (Np), with a reference counterpart of uncontrolled structure (Ref). The improved radial gases diffusion in the circles monolith design is confirmed, and nanoparticles show enhanced CO2 methanation activity than the uncontrolled-size active phase at low temperatures (< 300 ºC). On the contrary, the Ref catalysts achieve higher CH4 production at higher temperatures, where the reaction kinetics is controlled by mass transfer limitations (T > 300 ºC). SEM and Hg porosimetry evidence that nanoparticles are deposited at deeper penetration through the narrow micropores of the carbon matrix of the monolithic supports, which tend to accumulate on the channels surface remaining more accessible to the reactant molecules. Altogether, this study examines the impact of the channel tortuosity and the active phase sizing on the CO2 methanation activity, serving as ground knowledge for the further rational and scalable fabrication of carbon monolith for catalytic applications.

Efficient and robust ultrathin porous carbon encapsulated Ni–Sn intermetallic compounds derived from metal–organic frameworks for in-situ aqueous phase deoxygenation of fatty acid methyl esters

Deoxygenation of fatty acid esters in aqueous phase using in-situ generated H2 has emerged as a promising approach to producing sustainable diesel-like hydrocarbons. In this study, we employed a solvothermal method to synthesize novel Ni–Sn metal–organic frameworks (MOFs) with a homogeneous distribution of Ni and Sn elements. Subsequently, various Ni–Sn intermetallic compounds (IMCs) encapsulated with a porous carbon layer (<3 nm) (Ni–Sn IMC@C) were prepared through the facile pyrolysis of metal–organic frameworks under a controlled N2 atmosphere. Applying methyl palmitate as model reactant and methanol as hydrogen donor, Ni3Sn2 IMC@C gives approximately 100% conversion and 93% yield towards n-C15 and n-C16 alkanes at 330 °C, without significant deactivation during the recycling for five times. The deoxygenation pathway is dominated by decarbonylation (DeCO) on Ni–Sn IMCs. In Ni–Sn IMCs, the oxophilic nature of Sn, along with its charge transfer with Ni, enhances the adsorption of an η2(C, O)-aldehyde configuration. The strategic isolation of adjacent Ni by Sn effectively inhibits methanation and C–C bond hydrolysis, reducing H2 consumption and increasing carbon yield. Moreover, the ultrathin porous carbon encapsulation not only prevents the loss and sintering of Ni3Sn2 IMC under harsh hydrothermal condition but also mitigates mass transfer limitation. Surface oxidation of Ni3Sn2 IMC, particularly the formation of SnO2, is detrimental to deoxygenation. Additionally, Ni3Sn2 IMC@C exhibits high hydrocarbon yields (>89.6%) in in-situ aqueous phase deoxygenation of methyl laurate, methyl stearate and methyl oleate. These findings highlight the remarkable potential of MOF-derived catalysts for hydrothermal deoxygenation.

Robust enzyme-iron oxide nanoparticle composites entrapped in mesoporous silica nanospheres and their properties

Effective preservation of enzyme activity is required for using immobilized enzymes to catalyze reactions. To this end, the co-immobilization of an enzyme and nanoparticles in a nanosphere system using a reverse microemulsion is proposed. Iron oxide nanoparticles (MNPs) and carboxyl esterase (CE) were encapsulated in spherical mesoporous silica nanospheres. After immobilization, the encapsulated CE retained approximately 10.9% of the specific activity of free CE for the hydrolysis reaction. Regarding its stability during storage, the immobilized CE retained 52% and 30% of its initial activity after 30 days at 25 °C and under rigorous incubation conditions, respectively. Utilizing this magnetically separable property enabled the immobilized CE to be recycled 13 times through easy magnetic separation. The encapsulation of CE in silica nanospheres improved the efficiency of the enzymatic reactions by reducing the mass transfer limitation without any structural changes upon immobilization. This is the first demonstration of the co-encapsulation of MNPs and enzymes in mesoporous silica nanospheres to form stabilized and immobilized enzyme systems for biocatalytic applications.