Alkaline Catalyst Research Articles

Controlled fabrication of hierarchical porous carbon nanospheres with high doped nitrogen content for high-performance adsorbent of biomacromolecule

Constructing nitrogen-doped porous carbons with high specific surface area, rapid mass transfer channels, and positive charge is a crucial requirement for high-performance adsorbents. Herein, by the kinetic self-assembly synthesis strategy, we prepared nitrogen-doped hierarchical porous carbon spheres (N-HPCS) with adjustable pore structure, high specific surface area, and high nitrogen doping content (8.88 %). By using ethylenediamine as an assisted polymerization and assembly agent, the hydrolysis and condensation rate of tetraethyl orthosilicate (TEOS) as the silica source and the condensation rate of 3-aminophenol and formaldehyde as the phenolic resin precursor were controlled by adjusting ammonia volume as the alkaline catalyst to tune kinetic self-assembly of silica and phenolic resin components, thus achieving their simultaneous or sequential nucleus and growth. After carbonization and selective silica etching, three types of carbon nanospheres with center-radial pores, hollow center-radial pores and hollow structure were obtained. High nitrogen doping content endowed the nanospheres with positive charge. Through adsorption experiments on the bovine serum albumin (BSA) and Hemoglobin (Hb) as typical biological macromolecules, hollow carbon nanospheres with center-radial pores exhibited excellent adsorption performance for BSA(622.34 mg g−1) and Hb(759.96 mg g−1). Our fabricated N-HPCS may become a potential candidate for high-performance adsorption materials.

Catalytic Hydrothermal Treatment for the Recycling of Composite Materials from the Aeronautics Industry

Epoxy resin composite matrices reinforced with carbon fibers are highly demanded by certain industries such as the aeronautics industry because of their exceptional mechanical properties. Unfortunately, the use of reinforcing carbon fibers makes these composite materials hard to recycle by conventional methods. Therefore, in this study, specific hydrothermal treatments have been employed to recover carbon fibers from the offcuts of composite parts from the aeronautics industry. The resin decomposition rates (DRs) achieved by different settings of the operating parameters, such as the use of alkaline catalysts (KOH, NaOH, or K2CO3), the application of mechanical stirring, the use of different reaction times, the solvent volume/composite mass ratio, the specific surface area (surface area/mass) of the composite pieces, and the operating temperature and pressure (subcritical or supercritical conditions), have been examined and assessed. Under the conditions that have been evaluated, resin decomposition rates nearly as high as 98% have been achieved, while the recycled fibers retained over 95% of their original tensile strength (TS).

Enhancing biofuel production in hydrothermal liquefaction of cassava rhizome through alkaline catalyst application and water-soluble product recirculation

Hydrothermal liquefaction (HTL) possesses an outstanding biomass thermal conversion technology for producing biocrude oil (BO). Here, cassava rhizome (CR) was converted into BO via catalytic HTL using 1.0–10.0 wt% of K2CO3 and Na2CO3 with water-soluble product (WSP) recirculation at 275 °C for 15 min. The catalysts and WSP recirculation could enhance the BO fuel properties. The dominant BO yield of 38.00 and 34.80 wt% and HHV of 25.42 and 25.92 Mj/kg were derived using 4.0 wt% of K2CO3 and Na2CO3, respectively. Chemical compositions of the BO were principally phenols and hydrocarbons, which can be further upgraded and fractionated into alternative biofuels. On the other hand, the mass yield and HHV of the hydrochar (HC) co-product were reduced by the alkaline catalysts, while being maintained by WSP recirculation. The HC fuel characterization elucidated that the HC can be used as an alternative to coal. Furthermore, WSP characterization determined that organic acids were the major composition of the WSP. Thus, WSP recirculation can enhance CR decomposition according to the proposed reaction mechanism. These results indicate that the alkaline application and WSP recirculation constitute a dominant method for enhancing biofuel production via HTL.

Investigation into the Fuel Characteristics of Biodiesel Synthesized through the Transesterification of Palm Oil Using a TiO2/CH3ONa Nanocatalyst

Biodiesel is a renewable and sustainable alternative fuel to petrol-derived diesel. Decreasing the operating costs by improving the catalyst’s characteristics is an effective way to increase the competitiveness of biodiesel in the fuel market. An aqueous solution of sodium methoxide (CH3ONa), which is a traditional alkaline catalyst, was immersed in nanometer-sized particles of titanium dioxide (TiO2) powder to prepare the strong alkaline catalyst TiO2/CH3ONa. The immersion method was used to enhance the transesterification reaction. The mixture of TiO2 and CH3ONa was calcined in a high-temperature furnace in a range between 150 and 450 °C continuously for 4 h. The heterogeneous alkaline catalyst TiO2/CH3ONa was then used to catalyze the strong alkaline transesterification reaction of palm oil with methanol. The highest content of fatty acid methyl esters (FAMEs), which amounted to 95.9%, was produced when the molar ratio of methanol to palm oil was equal to 6, and 3 wt.% TiO2/CH3ONa was used, based on the weight of the palm oil. The FAMEs produced from the above conditions were also found to have the lowest kinematic viscosity of 4.17 mm2/s, an acid value of 0.32 mg KOH/g oil, and a water content of 0.031 wt.%, as well as the highest heating value of 40.02 MJ/kg and cetane index of 50.05. The lower catalyst amount of 1 wt.%, in contrast, resulted in the lowest cetane index of 49.31. The highest distillation temperature of 355 °C was found when 3 wt.% of the catalyst was added to the reactant mixture with a methanol/palm oil molar ratio of 6. The prepared catalyst is considered effective for improving the fuel characteristics of biodiesel.

Enhanced Vanadium Redox Flow Battery Performance with New Amphoteric Ion Exchange Membranes.

Vanadium redox flow batteries (VRFBs) depend on the separator membrane for their efficiency and cycle life. Herein, two amphoteric ion exchange membranes are synthesized, based on sulfonic acid group-grafted poly(p-terphenyl piperidinium), for VRFBs. Using ether-free poly(p-terphenyl piperidine) (PTP) as the polymer matrix, and sodium 2-bromoethanesulphonate (ES) and 1,4-butane sultone (BS) as grafting agents, We achieve quaternization of PTP through an environmentally friendly process without alkaline catalysts. PTP-ES and PTP-BS membranes exhibit low area resistance, high H+ permeability, and significantly reduced vanadium ion permeability, leading to exceptional ion selectivity, which is 3.06×106Smincm-3 and 4.34×106Smincm-3, respectively,three orders of magnitude higher than that of Nafion115 (0.27×104Smincm-3). The VRFB with PTP-BS achieves a self-discharge duration of 190h, compared to 86h for Nafion 115. Additionally, under current densities of 40-160mAcm-2, PTP-BS shows coulombic efficiencies of 98.1-99.1% and energy efficiencies of 92.0-82.1%, outperforming Nafion 115. The VRFB with PTP-BS also demonstrates excellent cycle stability and discharge capacity retention over 300 cycles at 100mAcm-2. Therefore, the amphoteric PTP-BS membrane shows remarkable performance, offering significant potential for VRFB applications.

Performance of oriented strand board bonded with a hybrid phenol-formaldehyde/polymeric methylene diphenyl diisocyanate adhesives system

A hybrid adhesive system composed of phenol-formaldehyde (PF) resin and polymeric methylene diphenyl diisocyanate (pMDI), modified with two types of alkaline catalysts, namely NaOH and CaCO3 at 20% (w/v), was used for manufacturing the oriented strand board (OSB) from sengon (Paraserianthes falcataria L. Nielsen) wood. The catalyst was added at a concentration of 1% of the solids content of PF adhesive, and pMDI was added at 2.5% and 5.0% of the PF adhesive solids content. Adding catalysts and cross-linking agents increased the solids content and viscosity of the adhesive and accelerated the gelation time. The water absorption of OSB increased with the addition of catalysts and crosslinking agents compared to the control PF. Still, the CaCO3 catalyst worked optimally in reducing the thickness swelling of OSB. The mechanical properties of the laboratory-fabricated OSB panels increased with the addition of catalyst and cross-linker, except for the modulus of elasticity parallel to the grain. The optimal performance of OSB was obtained by adding 1% CaCO3 and 2.5% pMDI based on the PF’s solids content.

Influence of Solid Alkaline Photocatalysts Irradiated with UV Light on Fuel Properties of Palm Oil Biodiesel.

TiO2 nanoparticles are full of porosity that can be impregnated with a strong alkaline catalyst CH3ONa to form a TiO2/CH3ONa catalyst. TiO2 of the anatase phase, which is a semiconductor material, has been a prominent photocatalyst due to its excited photocatalyst activity, chemical and biological stability, and nontoxicity. The CH3ONa compound has been widely used as a catalyst for transesterification. Although the synthesized photocatalyst TiO2 powder with CH3ONa is anticipated to greatly enhance the transesterification efficiency, leading to improving biodiesel properties, relevant studies have not been found. After the photocatalyst was prepared, a reactant mixture of palm oil, methanol, and heterogeneous catalyst TiO2/CH3ONa was illuminated by ultraviolet (UV) light from light-emitting diode (LED) lamps. The experimental results revealed that the formation of fatty acid methyl esters was significantly increased to 98.4% with ultraviolet-light illumination for the molar ratio of methanol/palm oil equal to 6 and 3 wt % catalyst addition. The decrease of the catalyst amount to 2 wt % resulted in a slight decrease of the fatty acid methyl esters to 97.06 wt %. The lowest kinematic viscosity and acid value and the highest distillation temperature, heating value, and cetane index were observed under the above reaction conditions. The distillation temperature and cetane index were increased while the acid value was decreased under ultraviolet illumination on the reactant mixture. Consequently, the optimum preparing conditions for biodiesel production were 6 and 3 wt % for the molar ratio of methanol/palm oil and catalyst addition under UV-light irradiation.

Sustainable Biodiesel Production from Waste Cooking Oil and Crude Palm Oil Using a Custom Mini Pilot Plant

The widespread practice of reusing Waste Cooking Oil (WCO) in hawker food stalls, often for multiple frying cycles, presents a significant public health concern due to the degradation of the oil, which can lead to the formation of toxic compounds. These practices not only pose health risks, such as increasing the potential for cardiovascular diseases and cancer, but also contribute to environmental pollution when the oil is improperly disposed of. This study seeks to address these issues by converting WCO, along with crude palm oil (CPO), into biodiesel using a custom-designed mini pilot plant. The biodiesel production process involved a two-step reaction. The first step, esterification, was conducted using a 55:100 alcohol-to-oil volume ratio with 1% by volume sulfuric acid (H₂SO₄) as the acid catalyst, at 60°C, with a reaction time of 30 minutes and a stirring speed of 800 rpm. The second step, transesterification, utilized a 6:1 alcohol-to-oil molar ratio, with 1 wt.% sodium hydroxide (NaOH) as the alkaline catalyst, carried out at 70°C over the course of one hour. These conditions were carefully selected to optimize the conversion efficiency and to minimize the free fatty acid content, which is crucial for achieving a high yield of biodiesel. The results demonstrated that the mini pilot plant is highly effective in producing biodiesel from both WCO and CPO. The study also led to the development of a standard operating procedure (SOP) for the biodiesel production process, ensuring reproducibility and efficiency.

Synthesis of base-acid pair based poly(isatin arylene) membranes for HT-PEMFC applications

Phosphoric acid (PA) doped polymer electrolyte membranes are promising high temperature proton exchange membranes (HT-PEMs) for fuel cells. While PA doped polybenzimidazole (PBI) has been considered as a successful HT-PEM, several issues remain, such as the use of carcinogenic monomer, poor solubility in organic solvents and easy PA loss. To develop more cost-effective, readily synthesized and high-performance HT-PEMs, this study focuses on synthesizing high-performance HT-PEMs based on poly(isatin arylene)s (i.e., PIT and PIB) containing a lactam structure and devoid of ether bonds. These polymers are synthesized from isatin and p-terphenyl (or biphenyl) under superacid catalysis. Subsequently, glycidyl trimethyl ammonium chloride (GTA) is employed as a grafting reagent for PIT and PIB. This ring-opening reaction is accomplished through an efficient and environmentally friendly procedure without any alkaline catalysts. The introduced GTA side chains with quaternary ammonium and hydroxyl groups not only produce microphase separation structures that facilitate proton conduction, but also reduce PA loss. Comparing with PIT-GTA with terphenyl units, the PIB-GTA membrane with short biphenyl units exhibits superior properties. For instance, the PIB-GTA/218.5%PA membrane achieves a high conductivity of 0.103 S cm−1 at 180 °C and a tensile strength of 6.6 MPa at room temperature. Without humidification and backpressure, the PIB-GTA/218.5%PA based H2–O2 single cell displays a peak power density of 632 mW cm−2 at 160 °C. This work presents a straightforward approach to synthesizing GTA grafted poly(isatin arylene) membranes for HT-PEM fuel cells.

Electrolysis Approach of Fatty Acid Methyl Ester Production Using Alkali Hydroxides and Their Alkoxides

The depletion of fossil fuels and environmental concerns have led to the search for alternative fuels (biodiesel) derived from renewable resources. Electrolysis is a promising method of fatty acid methyl ester (FAME) synthesis that can be maintained at room temperature. Nevertheless, the low reaction rates have been commonly accelerated using a combination of catalysts and electrolytes. This work proposed a novel electrolyte-free electrolysis approach for biodiesel synthesis from soybean oil using alkaline hydroxide (NaOH, KOH) and alkaline methoxide (NaOCH3, KOCH3)catalysts. Though all of them demonstrated high biodiesel yield, KOCH3 exhibitedthe highest efficiency. Based on response surface methodology, the highest FAME yield of 97.11% was achieved at optimal electrolysis voltage of 18.76V, water amount of 1.97 wt.%, KOCH3 amount of 3.17 wt.%, and methanol/oil of 21.33:1 molar, and reaction time of 60 min. The fuel properties of synthesized biodiesel agreed with international standards.The findings of this work suggest that electrolyte-free electrochemical using alkaline hydroxides and alkaline methoxides as catalysts could be a useful alternative to conventional transesterification method for producing biodiesel. Keywords: Alkaline catalysts, Biofuel, Box–Behnken Design, Electrochemical approach

Strength and Acid Resistance of Mortar with Different Binders from Palm Oil Fuel Ash, Slag, and Calcium Carbide Residue

This study deals with the use of ground palm oil fuel ash (GPOFA) in combination with ground granulated blast furnace slag (GGBFS) and ground calcium carbide residue (GCR) to produce the binary and ternary binders-based alkali activated mortar. The appropriate content of materials in each binder type was determined as a function of compressive strength. The results revealed that both GPOFA:GGBFS and GPOFA:GCR binders had an optimum blending ratio of 70:30 wt%, while the GPOFA:GGBFS:GCR binder was 55:30:15 wt%. An alkaline catalyst of NaOH was admixed to the best mixture in each binder type to stimulate the mortar's compressive strength. The sulfuric acid (H2SO4) resistance of the mortar in terms of weight change was also examined. The addition of 1M NaOH in both binary and ternary binders could enhance the compressive strength and H2SO4 resistance of the mortar. The highest compressive strength and lowest weight change due to soaking in H2SO4 solution were found in the ternary binder mortar with a 1 M NaOH. The mortar with GCR immersed in H2SO4 solution resulted in an increased weight, which was different from that of the mortar without GCR. The microstructural analysis of the alkali-activated pastes indicated more reaction products than in the case of the pastes without alkali activator. However, a higher concentration of 2 M NaOH resulted in a poor microstructure, which had a negative effect on the compressive strength and H2SO4resistance. Doi: 10.28991/CEJ-2024-010-07-08 Full Text: PDF

Microwave absorbing alkaline catalyst for biodiesel production via MIL-100(Fe): Catalytic optimization, characterizations, kinetics, and distillation simulation

Microwave heating (MW) is known for its efficacy in promoting transesterification for biodiesel production. However, the microwave-induced catalysis, linked to catalyst absorbing capability, remains poorly understood. Herein, a class of alkaline catalysts with strong microwave absorption were synthesized, validating their positive impact on transesterification. Various methods were used to reveal the relationship between microwave absorbing capacity and physicochemical properties of the synthesized catalyst (KF/Mg-MIL). Results indicated the previously recognized basicity’s role for KF/Mg-MIL was surpassed by microwave absorbing capability (permittivity and permeability) in MW (2.45 GHz). KF/Mg-MIL, with εr = 4.94′-j1.09″ and μr = 1.03′-j0.024″, efficiently transformed microwave into thermal energy via the dielectric loss and magnetic loss, saving 50 % energy consumption and reducing 1051.61 kg CO2 for per ton biodiesel compared to water bath heating (WB). Notably, “non-thermal” effect was observed with KF/Mg-MIL in MW, which reduced activation energy by 2.49 kJ/mol and increased the frequency factor by 793.32 min−1 in comparison to WB.

Interface Engineering via Ti3C2Tx MXene Enabled Highly Efficient Bifunctional NiCoP Array Catalysts for Alkaline Water Splitting.

Developing a non-noble metal-based bifunctional electrocatalyst with high efficiency and stability for overall water splitting is desirable for renewable energy systems. We developed a novel method to fabricate a heterostructured electrocatalyst, comprising a NiCoP nanoneedle array grown on Ti3C2Tx MXene-coated Ni foam (NCP-MX/NF) using a dip-coating hydrothermal method, followed by phosphorization. Due to the abundance of active sites, enhanced electronic kinetics, and sufficient electrolyte accessibility resulting from the synergistic effects of NCP and MXene, NCP-MX/NF bifunctional alkaline catalysts afford superb electrocatalytic performance, with a low overpotential (72 mV at 10 mA cm-2 for HER and 303 mV at 50 mA cm-2 for OER), a low Tafel slope (49.2 mV dec-1 for HER and 69.5 mV dec-1 for OER), and long-term stability. Moreover, the overall water splitting performance of NCP-MX/NF, which requires potentials as low as 1.54 and 1.76 V at a current density of 10 and 50 mA cm-2, respectively, exceeded the performance of the Pt/C∥IrO2 couple in terms of overall water splitting. Density functional theory (DFT) calculations for the NCP/Ti3C2O2 interface model predicted the catalytic contribution to interfacial formation by analyzing the electronic redistribution at the interface. This contribution was also evaluated by calculating the adsorption energetics of the descriptor molecules (H2O and the H and OER intermediates).

A Mini Review on the Influence of Different Intermediate Mass Transfer Effects on the Chemical Pretreatment of Lignocellulosic Biomass

ABSTRACTChemical pretreatment of lignocellulosic biomass (LCB) in the presence of an alkaline catalyst is one of the major pretreatment processes that recover cellulose, hemicellulose, and lignin at effective process conditions and also for the production of bioethanol. Replacement of conventional catalysts with waste‐derived catalysts in the pretreatment process will be helpful for the development of low‐cost biorefinery. The continuous impact of different mass transfer properties during the chemical pretreatment of LCB will affect the final yield of products at a high reaction time and has been reviewed in the current study. Intraparticle diffusion of an alkaline catalyst into LCB is going to determine the diffusion of the selected catalyst within the porous biomass structure, which helps in the enhancement of the final yield of the product recovery at low‐process conditions. The diffusion of the synthesized catalyst within the selected biomass during the chemical pretreatment process is a rate‐limiting step that influences the final recovery yield of desired products. Enhancement of the biomass pretreatment reaction through the assessment of the diffusivity using the modified Nernst–Einstein relation is also discussed. Determination of different unique mass transfer properties rate of diffusion, diffusivity flux, and mass transfer coefficient are also to be analyzed to advance the reaction rate of the pretreatment process.

Environmentally Friendly o-Cresol-Furfural-Formaldehyde Resin as an Alternative to Traditional Phenol-Formaldehyde Resins for Paint Industry.

This paper describes studies on the preparation of an o-cresol-furfural-formaldehyde resin in the presence of an alkaline catalyst and its modification with n-butanol or 2-ethylhexanol. The novelty of this research is to obtain a furfural-based resin of the resole type and its etherification. Such resins are not described in the literature and also are not available on the market. The obtained resin based on furfural, which can be obtained from agricultural waste, had a low minimum content of free o-cresol < 1 wt.%, furfural < 0.1 wt.%, and formaldehyde < 0.1 wt.%. The resin structure was characterized by mass spectrometry (ESI-MS), FT-IR, and NMR spectroscopy, which showed the presence of hydroxymethylene groups in the resin before modification and alkyl groups derived from n-butanol and 2-ethylhexanol after modification. The etherified resins had a lower viscosity and were more flexible (DSC) than the resin before modification and they can be used as an environmentally friendly, safe, and sustainable alternative to traditional phenol-formaldehyde resins in the paint industry. They demonstrate the ability to create a protective coating with good adherence to metal substrates and an excellent balance of flexibility and hardness.

Heterogeneous alkaline catalyst synthesized from local bovine bone wastes for transesterification of palm oil into biodiesel

Abstract Local bovine bone wastes, which are abundant in Aceh Province, have been successfully used as biomineral sources to produce heterogeneous catalysts that result in alkaline oxide. This study aimed to produce alkaline oxides by employing a high heat breakdown approach on local bovine bone particles at atmospheric pressure. The physicochemical analysis of the obtained inorganic particles revealed that the predominant component of those obtained inorganic oxide particles was calcium oxides (CaO). Furthermore, the produced alkaline oxide was employed as an alkali oxide catalyst for the transesterification of palm oil (RPDPO) with methanol, yielding methyl ester compounds, which are well recognized as a sustainable and green diesel energy source.

Optimization of Transesterification Process for Biodiesel Production using Jatropha Oil

Biodiesel has attracted considerable attention during the past decade as a renewable, biodegradable, and nontoxic fuel alternative to fossil fuels. Biodiesel can be obtained from vegetable oils (both edible and non-edible) and from animal fat. Biodiesel was produced through esterification of Jatropha oil using an alkaline catalyst. The process was carried out at the reaction temperatures of 63 and 55°C, with a 6:1-11:1 oil to methanol molar ratio, and the concentration was verified. In this research work, a yield of 91.78% and 80% was achieved. Furthermore, the flash point of 129.1°C obtained indicates that the biodiesel is within the specification of ASTM. Jatropha curcas Linnaeus, a multipurpose plant, contains a high amount of oil in its seeds which can be converted to biodiesel. J. curcas is probably the most highly promoted oilseed crop at present in the world. The availability and sustainability of sufficient supplies of less expensive feedstock in the form of vegetable oils, particularly J. curcas, and efficient processing technology to biodiesel will be crucial determinants of delivering competitive biodiesel. Oil contents, physicochemical properties, and fatty acid composition of J. curcas are reported in research. The fuel properties of Jatropha biodiesel are comparable to those of fossil diesel and conform to the ASTM standard. The objective of this review is to give an update on the J. curcas L. plant, the production of biodiesel from the seed oil, and research attempts to improve the technology of converting vegetable oil to biodiesel and the fuel properties of Jatropha biodiesel. There is also a need to carry out a lifecycle assessment and assess the environmental impacts of introducing large-scale plantations. Furthermore, there is still a dearth of research about the influence of various cultivation-related factors and their interactions and influence on seed yield. The formation of biodiesel was confirmed by FT-IR and GC-MS analysis, and the conversion of ester functional group into methyl esters was verified, and characteristic properties of biodiesel were successfully determined. Keywords: Biodiesel, Jatropha oil, transesterification, catalyst, optimization, renewable energy and sustainability

Prospect of Biodiesel from Sludge Palm Oil in Malaysia

High feedstock costs make biodiesel production impractical and economically unfeasible, particularly as most feedstocks are unknown for performance. Waste oil, such as sludge palm oil (SPO), may be used to produce biodiesel. This study examined the efficiency and prospect of Sludge Palm Oil Biodiesel (SPOB) production from SPO through transesterification. One-step and two-step transesterification methods were performed for SPOB conversion. However, only a two-step method was effective in converting SPO into SPOB. SPO's high free fatty acid (FFA) content necessitated a two-step process to reduce FFAs to less than 4% before SPOB conversion. Step 1 yielded 78% SPOB at 2 hours, 0.03:1 acid catalyst–to–oil, and 8:1 alcohol–to–oil. The optimal SPOB yield for step 2 at 4 hours, 0.01:1 alkaline catalyst–to–oil, and 9:1 alcohol–to–oil was 78%. SPOB components were analyzed using FTIR with SPOB having a 1435.04 cm-1 methyl peak. The diesel engine performance test mixed SPOB with mineral diesel at different concentrations with 30% SPOB blends in mineral diesel offers the lowest fuel consumption (0.1089 ml/s), maximum braking horsepower (24.9266 rpm), and best mechanical efficiency. Density, flash point, and heating value were also tested to identify SPOB's physical characteristics and discussed in detail.

Kinetic Regularities of the Synthesis of Silica Nanoparticles by Heterogeneous Hydrolysis of Tetraethoxysilane Using L-Arginine as a Catalyst

Abstract The kinetics of the synthesis of silica nanoparticles (&lt;50 nm) has been studied under the conditions of heterogeneous hydrolysis of tetraethoxysilane (TEOS) using L-arginine as an alkaline catalyst. The rates of silica formation have been determined in a temperature range of 10–95°C at catalyst concentrations of 6–150 mM. It has been shown that the activation energy of the process depends on catalyst concentration and varies in a range of 21.5–13.9 kJ/mol, while decreasing linearly with increasing concentration of L-arginine in the system. The criterion of maintaining the monodispersity has been estimated for SiO2 particles being grown “onto seeds.” The density of submicron-sized silica particles has been experimentally determined as depending on the annealing temperature. Within a temperature range of 200–1000°C, the particle density varies from 2.04 to 2.20 g/cm3.

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 (0.05 g) with complete conversion of glucose (28 mM) at 140 ℃, 2 MPa N2 for 10 h. 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.