Strong Solid Base Research Articles

Fabrication of Strong Basic Sites on Cr3+ Doped Reductive Support and Its Catalytic Application for Transesterification

Solid strong base catalysts have attracted much attention for their excellent catalytic performance and environmental friendliness due to heterogeneous properties. However, this kind of catalyst usually needs a higher temperature to be activated. Therefore, it is still a challenge to obtain high-activity catalysts at lower fabrication temperatures. In this paper, a reductive catalyst support containing low-valence metal centers (Cr3+) was prepared. Through the redox reaction between the Cr3+ and KNO3, the basic sites can be produced at lower temperatures on the reductive support (Cr-MeIM). Thermogravimetry-mass (TG-MS) spectrometer results showed that the base precursor began to be transformed into basic sites at about a low temperature of 180°C. The solid base catalyst was applied into transesterification between ethylene carbonate (EC) and methanol. By using 0.05 g of catalyst for 3 h at 70°C, we obtained a dimethyl carbonate (DMC) yield of up to 60.9%, which means that the catalyst has high activity.

Atomically dispersed calcium as solid strong base catalyst with high activity and stability

Solid strong base catalysts are highly attractive for diverse reactions owing to their advantages of neglectable corrosion, facile separation, and environmental friendliness. However, their widespread applications are impeded by basic components aggregation and low stability. In this work, we fabricate single calcium atoms on graphene (denoted as Ca1/G) by use of a redox strategy for the first time, producing solid strong base catalyst with high activity and stability. The precursor Ca(NO3)2 is first reduced to CaO at 400 °C by the support graphene, forming CaO/G with conventional basic sites, and the subsequent reduction at 850 °C results in the generation of Ca1/G with atomically dispersed Ca. Various characterizations reveal that Ca single atoms are anchored on graphene in tetra-coordination (Ca–C2–N2) where N is in situ doped from Ca(NO3)2. The atomically dispersed Ca, along with their anchoring on the support, endow Ca1/G with high activity and stability toward the transesterification reaction of ethylene carbonate with methanol. The turnover frequency value reaches 128.0 h−1 on Ca1/G, which is much higher than the traditional counterpart CaO/G and various reported solid strong bases (2.9–46.2 h−1). Moreover, the activity of Ca1/G is well maintained during 5 cycles, while 60% of activity is lost for the conventional analogue CaO/G due to the leaching of Ca.

Generation of Strong Basicity in Metal-Organic Frameworks: How Do Coordination Solvents Matter?

Solid strong bases with an ordered pore structure (OPS-SSBs) have attracted much attention because of their high catalytic activity and shape selectivity as heterogeneous catalysts in various reactions. Nevertheless, high temperatures are required to fabricate OPS-SSBs by using traditional methods. Herein, we report for the first time that the coordination solvents affect basicity generation in metal-organic frameworks (MOFs) greatly and that strong basicity can be formed at comparatively low temperatures. A typical MOF, MIL-53, was employed, and three different solvents, namely, water, methanol, and N,N-dimethylformamide (DMF), were coordinated, respectively, by means of solvent exchange. Thermogravimetry-mass spectrometer analysis shows that the conversion temperature of base precursor KNO3 is quite different on MIL-53 coordinated with different solvents. The conversion of KNO3 to basic sites takes place at 350, 300, and 250 °C on MIL-53 coordinated with water, methanol, and DMF, respectively. It is fascinating to observe the generation temperature of strongly basic sites at 250 °C, which is noticeably lower than that on various supports, such as mesoporous silica SBA-15 (600 °C), zeolite Y (700 °C), and metal oxide ZrO2 (730 °C). This is due to the redox interaction between coordination solvents and KNO3, leading to a significant decrease in the temperature for KNO3 conversion. Consequently, OPS-SSBs were prepared successfully with an ordered pore structure and strong basicity. The obtained OPS-SSBs show good shape selectivity in Knoevenagel condensation of aromatic aldehydes with different active methylene compounds. Moreover, these solid bases are highly active in the synthesis of dimethyl carbonate through transesterification reaction. This work might open up a new avenue for the fabrication of various functional materials at low temperatures through redox interactions.

Direct production of biodiesel from waste oils with a strong solid base from alkalized industrial clay ash

Biodiesel was directly one-step produced from waste oils without pretreatment catalyzed by a solid base alkalized from spent bleaching clay (SBC) ash. Optimized conditions were obtained with 99.1% biodiesel yield from soybean oil with an orthogonal design. The base catalyst was stable within 8 cycles (>95% biodiesel yield) and resistant to saponification (AV = 9.7 mg KOH/g, 96.5% biodiesel yield). The base was characterized with XRD, EDX-mapping, FT-IR, XRF and TPD, and it had similar strong basicity to Na2SiO3 (0.21 vs. 0.22 mmol/g for Na2SiO3) with active sites of Na2O and CH3ONa evolved from Na2SiO3 and NaAlSiO4 by reactions of NaOH with oxides (e.g., SiO2, Al2O3) in SBC ash. Furthermore, the base was magnetized with magnetism of 6.86 emu/g by carbonizing residual oil in SBC as carbon support and reductant (of Fe2O3 to magnetic Fe3O4 particles). It catalyzed soybean oil to produce biodiesel with 99.2% yield and blended oil (AV = 5.9) to biodiesel with 91.9% yield without any saponification. The catalyst was magnetically separated and reused for 3 cycles with 87% yield. The non-magnetic base could also efficiently catalyze actual SBC oil for the production of biodiesel with 95% yield at AV of 10. This work realized the full use of inorganics in SBC, and its oil for direct biodiesel production at a low temperature (i.e., 65 vs. 120 °C with sulfuric acid process) without wastes produced and results can easily find practical applications for waste oils.

Synthesis of a Stable, Water‐Tolerant, Short Mesoporous Organic Biguanide, Strong Solid Base and Its Application in Catalysis

AbstractFirstly, both a short mesopore thin plate molecular sieve of Zr‐doped SBA‐15 and a strong organic base of bi‐guanides DIC‐TMG were respectively prepared. Then, the organic bi‐guanides DIC‐TMG was grafted onto the short mesopore thin plate molecular sieve to prepare a highly efficient and stable water‐tolerant short mesoporous organic bi‐guanides strong solid base DIC‐TMG/Zr‐SBA‐15 which was used to catalyze the transesterification of renewable bio‐oils to biodiesel under mild reaction conditions. The prepared DIC‐TMG/Zr‐SBA‐15 was elaborately investigated by XRD, BET, SEM, TEM, FT‐IR and Elemental analysis. The obtained results showed that compared with TMG/Zr‐SBA‐15 and DIC‐TMG/SBA‐15, DIC‐TMG/Zr‐SBA‐15 exhibited the best catalytic activity with 95% of biodiesel yield at reaction temperature 75 °C and catalyst dosage 5 wt%. Especially, unlike some other usually solid metal‐based catalysts, this alkaline organic bi‐guanidines DIC‐TMG supported on Zr‐SBA‐15 support catalyst has certain water‐tolerant. With 1 wt% of water content existed in the reaction system, the biodiesel yield still reached 90%, and after five recycles of the catalyst, the biodiesel yield was still more than 80%.

Hydrophobic strong solid base derived from graphene oxide hybrid zirconium MOFs and its enhanced stability on furfural-MIBK aldol condensation to synthesize branched biofuel precursors

Aldol condensation between furfural (FA) and MIBK is used to synthesize branched bio-jet-fuel precursors. It remains difficult to design hybrid solid bases to efficiently promote this reaction, because only strong basic sites can activate MIBK. Different basic species were immobilized into zirconia/carbon hybrid supports by thermal decomposition of GO/UiO materials loaded with corresponding alkane (earth) nitrides. Only Cs immobilized zirconia/carbon (CsZC) could efficiently promote this reaction, while counterparts with Li, Mg and Ca species showed little activity over condensation between MIBK and FA. Optimized CsZC showed excellent FA conversion and selectivity towards desired products (88.6% in yields of FMIBK in 6 h at 130 °C). Two indirect proofs were provided to check the influence of basic strength on the catalytic performance, and only Cs samples had enough strong basic sites to accelerate the reaction. After modified with octyl groups, hydrophobic CsZC were reused for 4th cycle while retaining most of its original activity. Functionalization with organosilanes increased the hydrophobicity of the surface, which had dramatical promotion on activity, selectivity, and stability. It was the first time to run recycling experiments for this reaction, to afford the demands for chemical sustainability.

Fabrication of Strong Solid Base FeO–MgO for Warm CO2 Capture

A strong solid base, FeO–MgO, is synthesized using magnesium acetate and ferrous acetate in order to meet the requirement of capturing CO2 in flue gas at a temperature higher than 423 K. After the two salts are ground and carbonized at 823 K, the ferric MgO composite with a surface area exceeding 160 m2 g−1 is obtained, where ferric oxide species are wrapped by magnesia particles. The influence of ferric salt on the structure and adsorption properties of the strong solid bases is investigated to determine the optimal amount, and the distribution of ferric additive is assessed with X‐ray diffraction (XRD) and X‐ray photoelectron spectroscopy (XPS). With a mass ratio of ferrous oxide of about 3%, the basic sorbent could capture 35 mg g−1 CO2 at 473 K and the ratio of strong base sites increases to 91%. Both the CO2 adsorption capacity and the ratio of strong basic sites are higher than those of the other MgO sorbents, which is beneficial for warm CO2 capture. Additionally, the function of strong basic sites in the ferric MgO sorbent is explored in the instantaneous adsorption of warm CO2. The capability in the cycled warm CO2 adsorption is found to be related to the desorption temperature of CO2. Different forms of CO2 injections are used in adsorption and the influence on the performance of the strong basic sorbent is also studied.

Polyvinyl amine as a modified and grafted shell for Fe3O4 nanoparticles: As a strong solid base catalyst for the synthesis of various dihydropyrano[2,3-c]pyrazole derivatives and the Knoevenagel condensation

In this work, we reported one-step deposition of polyacrylamide on nano-magnetite surface via a simple and in situ polymerization of acryl amide to form n-Fe3O4/PAM nanocomposite. The amide (–CONH2) groups could be converted easily to amine (–NH2) groups through Hofmann degradation to introduce n-Fe3O4/PVAm as a highly efficient heterogeneous base catalyst. The obtained organic-inorganic nanocomposite exhibited high catalytic activity for the solvent-free syntheses of various dihydropyrano[2,3-c]pyrazole derivatives and the Knoevenagel condensation in high to excellent yields and in the following, a plausible mechanism for the synthesis of them has been proposed. Because of the polymer layer coated Fe3O4 nanoparticles, the catalyst has many catalytic units, and acceptable thermal stability and recyclability. Titration, FT-IR, SEM, TGA, VSM, and XRD analysis were used for characterization of the catalyst. Also, the nanocomposite can be easily recovered by a magnetic field and reused up to 9 times without distinct deterioration in catalytic activity.

Calcium oxide-modified mesoporous silica loaded onto ferriferrous oxide core: Magnetically responsive mesoporous solid strong base

The design of new type of solid strong base with ideal activity, stability, and reusability is strongly urged by the growing demand of green chemistry and sustainable development. In this study, a new type of mesoporous solid strong base, denoted as CaO/mSiO2/Fe3O4, is successfully fabricated by successively coating SiO2 onto Fe3O4 magnetic nanoparticles and loading CaO into the mesoporous SiO2. Compared with a series of other typical solid bases, the CaO/mSiO2/Fe3O4 exhibits higher activity towards the synthesis of dimethyl carbonate by the transesterification of ethylene carbonate and methanol. The activity of the CaO/mSiO2/Fe3O4 is not observed to decrease obviously even after sextic catalyst recirculation, and in particular, the recovery of the catalyst without quality loss is very convenient due to the good magnetic responsiveness of the Fe3O4 cores.

Solid strong base K-Pt/NaY zeolite nano-catalytic system for completed elimination of formaldehyde at room temperature

Solid strong base nano-catalytic system of K-modification NaY zeolite supported 0.08% Pt (K-Pt/NaY) were constructed for eliminating HCHO at room temperature. In the catalytic process, activation energy over K-Pt/NaY nano-catalytic system was greatly decreased along with the enhanced reaction rate. Characterization and catalytic tests revealed the surface electron structure of K-Pt/NaY was improved, as reflected by the enhanced HCHO adsorption capability, high OH concentration, and low-temperature reducibility. Therefore, the optimal K-Pt/NaY showed high catalytic efficiency and strong H2O tolerance for HCHO elimination by directly promoting the reaction between active OH and formate species. These results may suggest a new way for probing the advanced solid strong base nano-catalytic system for the catalytic elimination of indoor HCHO.

Strong base g-C3N4 with perfect structure for photocatalytically eliminating formaldehyde under visible-light irradiation

Solid strong base systems of g-C3N4 by inducing potassium (KC3N4) were constructed for photocatalytically decomposing HCHO. Characterization and theoretical calculation revealed that the formation of K-C and K-N perfected the π-conjugated structure of g-C3N4, which greatly enhanced the basicity, improve optical and electrical properties of g-C3N4. In the photocatalytic process, K-improved π-conjugated structure promoted HCHO adsorption, activation, completely oxidative decomposition under visible-light irradiation. Therefore, KC3N4 photocatalysts presented high efficiency in photocatalytic elimination of HCHO, and the optimal apparent rate reached 0.21 mol−0.17 L0.17 min−1 with 1.17 reaction order by promoting the reaction between active oxygen (OH and OH) and formate species under visible-light irradiation, which was 30 times of that (0.007 mol−0.17 L0.17 min−1) over pristine g-C3N4. These results may suggest a new way for probing the advanced solid strong base photocatalysts for eliminating volatile organic compounds.

Potassium-incorporated mesoporous carbons: strong solid bases with enhanced catalytic activity and stability

Through chemical activation combined with the hard-templating strategy, potassium-incorporated mesoporous carbons were fabricated which showed strong basicity and enhanced catalytic performance.

Acquiring an Efficient Warm‐CO2 Sorbent from Advanced Pyrolysis of Magnesium Oxalate

AbstractFor the first time, porous MgO with a Brunauer–Emmett–Teller (BET) surface area over 200 m2 g−1 can be simply obtained from pyrolysis of common magnesium oxalate without any solvent or additive. The obtained porous MgO had a large surface area of 278.5 m2 g−1 and captured 30.8 mg g−1 of CO2 in the instantaneous adsorption at 473 K, comparable with many MgO‐based sorbents prepared through complex procedures. Use of a U‐pipe furnace along with the specific “throughout” sweeping mode of nitrogen carrier gas enable this efficient warm‐CO2 sorbent to be fabricated in a simple way. Factors including contacting modes between precursor salt and flowing gas, flow rate, type of gas and salt were carefully studied, and related to the pore structure and adsorption character of the MgO samples. Apart from the capability of trapping CO2 mixed with SO2 and NO at 473 K, the MgO sample showed a high ratio of exposed strong basic sites (70.5 %), which provides a useful solid strong base for control of CO2 in flue gas.

Preparation and characterization of a strong solid base from waste eggshell for biodiesel production

A strong solid base catalyst was prepared from waste eggshell by KF modification and thermal treatment. The eggshell catalyst was characterized by Fourier-transform infrared spectra (FT-IR), X-ray diffraction (XRD), scanning electron microscope (SEM) and solid-state nuclear magnetic resonance (NMR) spectroscopy. The characterization results show that potassium hydroxide (KOH) formed from the modification process enhances the basicity and catalytic ability of the catalyst. The solid base catalyst from eggshell (SBES) exhibits excellent catalytic activity and stability in the transesterification reaction, which suggested that this catalyst would be potentially used as a solid base catalyst for biodiesel production.

Mesoporous strong base supported cobalt oxide as a catalyst for the oxidation of ethylbenzene

A mesoporous solid strong base was applied to support cobalt oxide to obtain a strong base-type catalyst, which showed good performance in the heterogeneous oxidation of ethylbenzene under solvent-free conditions in the temperature range of 373–403 K. It was demonstrated that the reported strong base-type catalyst could facilitate the decomposition of 1-phenyl-ethylhydroperoxide, and a high reaction rate (2.89 × 10−5 s−1) could be obtained at 403 K.

Hierarchical high-silica zeolites as superior base catalysts

For more than four decades, the design of zeolite base catalysts has relied on the application of aluminium-rich frameworks exchanged with alkali metal cations (preferably Cs+). However, moderate activity associated with access and diffusion limitations, and high manufacturing costs associated with high caesium content (typically over 30%) have hampered their industrial implementation so far. Herein, we have discovered that high-silica USY zeolites outperform their Al-rich counterparts in a variety of base-catalysed reactions of relevance in the fine chemical industry, as well as in the upgrading of biofuels. The benefits of this class of materials are amplified upon the alleviation of diffusion constraints through the introduction of a network of intracrystalline mesopores by post-synthetic modification. For example, the resulting cation-free hierarchical USY provides an up to 30-fold Knoevenagel condensation activity compared to the benchmark Cs–X, and similar observations were made upon application in liquid-phase (nitro)aldol reactions. Moreover, in the gas-phase aldol condensation of propanal, high-silica zeolites provide superior activity, selectivity, and lifetime compared to caesium-containing zeolites and even a strong solid base such as MgO. We decouple the complex interplay between mesoporosity and intrinsic zeolitic properties such as crystallinity, and quantify the increase in catalyst effectiveness upon hierarchical structuring as a function of reactant size. The obtained results are a major step to resolve the drawbacks of zeolites catalysis and thereby revitalise their potential for industrial application.

Isolated lithium sites supported on mesoporous silica: a novel solid strong base with high catalytic activity.

Isolated lithium sites were anchored on mesoporous silica by a molecular precursor approach at room temperature. The resultant materials exhibit ordered mesostructure, high base strength, and more importantly, a molecular-level dispersion of active sites, which are extremely desirable for catalysis and impossible to be realized by conventional methods.

Controlled Synthesis of Different Morphologies of MgO and Their Use as Solid Base Catalysts

MgO is one of the most promising solid base catalysts and has attracted much attention because of its superior performance. The extent of catalytic properties of MgO is highly controlled by its morphology, particle size, crystalinity, and surface area. Here, the synthesis of MgO with different morphologies, such as random nanoflakes, arranged nanoflakes toward flower and house of card structure spheres, cubes, and hexagonal plates, through the calcination of magnesium carbonate hydrates (MCH) intermediate is presented. The intermediate MCH has been synthesized under hydrothermal or supercritical hydrothermal as well as solvothermal treatment of clear solution of Mg(NO)3, (NH4)2CO3, or nesquehonite rods in different pH's and amounts of free carbonate ions. A probable reduction mechanism is proposed to explain the formation of the MCH morphologies. The amount of carbonate ion has crucial role in the formation of different morphologies in hydrothermal condition. On calcinations of the synthesized MCH morphologies resulted in MgO with almost identical morphologies as parental MCH. The microstructures of calcined MgO are porous and made of MgO nanoparticle building blocks of the size 4–6 nm. The formed MgO nanoparticles consists of large number of edges and corners, step edges and step corners and numerous base sites of various strength (surface hydroxyl groups, low coordinate O2- sites) which are recognized as active basic sites in heterogeneous catalysis. The calcined MgO microstructures function as a strong solid base catalyst for the solvent-free Claisen-Schmidt condensation of benzaldehyde with acetophenone giving 99% conversion in 4 h. The MgO catalysts are easily recyclable with no significant loss in catalytic activity in the subsequent cycles.

Basic properties of MgLaO mixed oxides as determined by microcalorimetry and kinetics

The surface properties of magnesias and of La oxides supported on MgO and MgAl hydrotalcites were compared, using the adsorption of carbon dioxide followed by microcalorimetry. The differential heat of adsorption of CO 2 as a function of coverage is the same for MgO of different surface areas, ranging from 30 to 590 m 2/g, showing that the average coordination of Mg does not change, in agreement with the results reported for the structure of these materials. In the case of La catalysts, an effect of the support is noticed on the distribution of basic strengths, with a higher basicity for MgLa mixed oxides. MgAlLaO mixed oxide is also a strong solid base in spite of much lower La content. These catalysts are active for the transesterification of soybean oil with methanol at 338 K, using a ratio methanol/oil = 6, and give a rate comparable to that reported for anchored guanidines, considered as superbases.

Magnesia-Incorporated Mesoporous Alumina with Crystalline Frameworks: A Solid Strong Base Derived from Direct Synthesis

By use of a surfactant templating method, the direct synthesis of magnesia-incorporated mesoporous alumina (mMgAl-γ) was realized via self-assembly of inexpensive inorganic salts. The structural and basic properties of the obtained materials were well characterized by various approaches. The results show that mMgAl-γ samples possess strong basicity with excellent water-resistant ability, well-defined mesoporous structure, and γ-Al2O3 crystalline frameworks. In comparison with wet impregnation that leads to structural damage, the direct synthesis strategy allows the mesoporous alumina to maintain good mesostructure. For example, the Brunauer−Emmett−Teller surface area of sample mMgAl(0.1)-γ can reach 328 m2·g−1, which is obviously higher than that of the sample prepared by a conventional impregnation method (239 m2·g−1). Further investigations evidence that the fabrication of suitable preassembled mesoporous precursors is crucial for the efficiency of the present direct synthesis strategy. In the process o...