Strong Lewis Acid Sites Research Articles

Influence of WO3 Content in Phosphated Tungsten-Zirconium Oxide Catalysts on the Catalytic Pathways of Glycerol Transformation.

The catalytic performance of phosphate-stabilized WOx-ZrO2 compositions in gas-phase glycerol dehydration has been investigated. Results show that varying WO3 concentrations direct the process towards either acrolein or allyl alcohol formation. Catalysts with low WOx content exhibit strong Lewis acid sites (Zr4+ and W6+), where these metal ions likely function as redox sites, facilitating glycerol hydrogenolysis to produce allyl alcohol. Higher WO3 concentrations (exceeding 20 wt.%) lead to the shielding of some W6+ and Zr4+ sites by polytungstate surface complexes, which are strong Brønsted acid sites. This alteration promotes glycerol dehydration through the removal of two water molecules, thereby shifting the selectivity towards acrolein formation.

Sulfur-doped CuCo2O4 as a PMS activator: The synergy of oxygen defects and strong Lewis acid sites in boosting the elimination of ciprofloxacin

Herein, the synthesis of sulfur-modified CuCo2O4 (S-CuCo2O4) nanoparticles as a heterogeneous catalyst for peroxymonosulfate (PMS) activation was reported. The S-CuCo2O4 maintained the spinel structure and exhibited rich oxygen vacancies. Also, the presence of S atoms enlarged the specific surface area and created strong Lewis acid sites that both enhanced the adsorption ability toward PMS and CIP. Compared to the corresponding S-doped single oxides and CuCo2O4, the S-CuCo2O4 with the designed molar ratio of S and metal ions to be 10%, i.e., CCS-10, significantly improved the catalytic activity, indicating the synergism between Cu-O-Co bonds, the oxygen vacancies, and the Lewis acid sites. Under the optimal conditions of 0.1g.L-1 CCS-10 dosage, 0.2g.L-1 PMS, and natural pH, the CCS-10/PMS system could remove approximately 87% of CIP and 70% of TOC within 20min at a four-time higher rate than that of the pristine catalyst. This system showed the highest performance in the pH range from weak acidic to weak basic (pH 5.5 - pH 8.5). CCS10/PMS also displayed considerable efficiency in degrading various pollutants belonging to different categories (methylene blue (MB), carbamazepine (CBZ), bisphenol A (BPA), and sulfamethoxazole (SMX)). SO4•–, •OH, O2•–, and 1O2 active species were found to be responsible for CIP elimination. Finally, the PMS residual concentration was recorded to be 0.01g.L-1 after the reaction. Overall, this study could contribute a possible strategy to enhance the heterogeneous catalysts for the removal of organic pollutants.

A modified separator based on ternary mixed-oxide for stable lithium metal batteries

Li metal batteries (LMBs) are among the most promising options for next-generation secondary batteries under the rapidly growing demand for high-energy–density electrochemical energy storage. However, the implementation of LMBs are hindered by major obstacles such as dentritic Li deposition and low cycling Coulombic efficiency. A practical functional separator is developed in this study, which consists of a Lewis acidic mixed oxide of ZrO2-SiO2-Al2O3 as a functional coating with anion anchoring ability to modulate ion transport in the vicinity of the Li metal anode, delivering a high Li+ transference number of 0.88 in carbonate electrolytes that suppresses dendrite formation. The strong Lewis acid sites in ZrO2-SiO2-Al2O3 originate from coordinatively unsaturated Zr4+ ions, which immobilize anions and reduce their decomposition rate. This significantly improves the chemical stability of the electrolyte and induces a more stable solid electrolyte interphase layer. The modified separator enables an anode-free cell containing a high-loading LiNi0.8Co0.1Mn0.1O2 cathode to present stable charge and discharge cycling for 150 cycles at 0.5C. By effectively suppressing Li dendrite growth and supporting the long-term operation of anode-free LMBs, this study offers a novel approach to rationally design mixed oxides with high Lewis acidity for functional separators.

Lignin-MOF hybrid polymetallic composites for selective hydrogenolysis of cellulose derived 5-hydroxymethylfurfural

The development of green, effective and inexpensive catalysts was important for the catalytic transfer hydrogenation of 5-hydroxymethylfurfural (HMF) to prepare 5-methylfurfuryl alcohol (MFA). The assembly of sodium lignosulfonate (LS) with NiCo-MOFs through a simple hydrothermal method was reported, and a series of iron-containing polymetallic hybrid catalysts were investigated. The introduction of iron led to the increase of medium strong acid sites and Lewis acid sites in the catalyst and enhanced the adsorption of furan rings, thus improved the catalytic activity. The effects of calcination temperature, iron content, and reaction parameters (including reaction temperature, pressure, hydrogen donor solvent) were all studied in detail. It was found that HMF could be completely converted over Fe@Ni3Co-MOF-LS, with a MFA yield of 88.75 % under the optimal condition (240 ℃, 2 MPa N2 in 4 h) without the presence of hydrogen. This study provided a new perspective for the utilization of lignin resource as carbon-based catalysts for the production of biomass-derived platform chemicals.

Hydrogenation of inert aromatic compounds under mild conditions catalyzed by confined trimetal sites in porous metal silicate materials

Complete hydrogenation of aromatic compounds is an important subject in various industry fields. However, due to the high stabilization energy of aromatic compounds resulting from their high aromaticity and non-polarity, the hydrogenation reaction is usually performed under harsh reaction conditions in the presence of noble metal-based catalysts. We report herein a porous metal silicate (PMS) material PMS-58, which consists of Cu, Ce and Co trimetal active sites, demonstrating high catalytic activity and selectivity in hydrogenating of a series of aromatic compounds under mild conditions (60 °C and 0.5 MPa H2). PMS-58 is superior to the previously reported non-noble metal-based catalysts and could be favorably compared to noble metal-based catalysts. The unique catalytic properties of PMS-58 are derived from the synergistic work of trimetal sites with Ce species serving as strong Lewis acid sites for dissociation of dihydrogen, Co species stabilizing Cu(I) species, and Cu(I) species playing a crucial role in activating aromatic rings. Therefore, this work provides a new approach in developing highly efficient non-noble metal catalysts for complete hydrogenation of arenes under mild conditions, which could be applied in removal of aromatic compounds in petroleum products.

Tandem catalytic conversion of glucose and cellobiose to 5-ethoxymethylfurfural with record yields

The conversion of biomass-derived carbohydrates to 5-ethoxymethylfurfural (EMF) is a fascinating reaction with 100% carbon atom utilization. Although effective conversion of 5-hydroxymethylfurfural (HMF) and fructose to EMF have been achieved, the direct conversion of glucose only gave low EMF yields. Herein, we reveal that the combinations of common Lewis acid with Brønsted acid in ethanol universally catalyze rapid etherification of glucose to intractable ethyl glucoside (EGL), as impedes the further conversion toward the desired products. The synergy of large-pore tin phosphate (SnPO) bearing strong Lewis acidic sites with acidic ionic liquid 1-(4-sulfobutyl)-3-methylimidazolium chloride (BSO3HMIMCl) enable tandem catalytic conversion of glucose, cellobiose and starch to EMF with record yields (61.7%, 61.8% and 55.7%, respectively), far exceeding previous reports. This transformation probably occurs via multiple parallel pathways, where water molecules generated by dehydration cooperate with acid and Cl- to hydrolyze EGL back to glucose, thus forming a positive feedback on EMF production.

Activation of cotton with transition metal-based chlorides: Correlation of generation of pore structures with evolution of oxygen-containing species

Lewis acidity of chlorides is known to significantly impact fragmentation/condensation reactions in activation of biomass. Herein, activation of cellulose-rich cotton with CuCl2, ZnCl2 or FeCl3, the chlorides with low to strong Lewis acidity, was performed and the influences of varied chlorides on evolution of the pyrolytic products and pore structures of activated carbon (AC) were studied. The results indicated that ZnCl2 and FeCl3 with strong Lewis acidic sites catalyzed condensation of reaction intermediates of light or heavier ones to form AC with yield higher than that from cotton pyrolysis by 6.7 % and 53.3 %, respectively. Increasing AC production was mainly due to retainment of more oxygen (23.8 % of oxygen content for AC-FeCl3 and 20.7 % for AC-ZnCl2 versus 11.5 % from blank experiment). CuCl2 with weak Lewis acidity promoted dehydration of sugary structures, forming more sugar-derivatives in bio-oil but diminished production of AC. However, higher Lewis acidity does not meant higher capability for creating pores. Specific surface area for AC-ZnCl2-500 was much bigger than that of AC-FeCl3-500 (1783.9 versus 22.8 m2/g). Characterization of the activation with in-situ IR indicated that ZnCl2 catalyzed rapid dehydration of -OH and condensation of carbonyls below 500°C, transforming oxygen in stable C-O-C form and carbon in olefinic CC form for maintaining generated pore structures.

Variation in Catalytic Efficacies of a 2D pH-Stable MOF by Altering Activation Methods.

Although it is well-known that the Lewis acidity of Metal-Organic Frameworks (MOFs) can effectively enhance their catalytic activity in organic transformations, access to these Lewis-acidic sites remains a key hurdle to widespread applications of Lewis-acidic catalysis by MOFs. Easy accessibility of strong Lewis acidic sites onto 2D MOFs by using proper activation methods can be a cornerstone in attaining desired catalytic performance. Herein, we report a new 2D chemically stable MOF, IITKGP-60, which displayed excellent framework robustness over a wide pH range (2-12). Benefiting from the abundant open metal sites (OMSs) and framework robustness, the catalytic activity of the developed material was explored in one-pot three-component Strecker reaction and Knoevenagel condensation reaction. Moreover, the developed catalyst is superior in catalyzing the reactions involving sterically hindered substrate (1-naphthaldehyde) with high turnover number. A comparative catalytic study was conducted using different activation methods (chloroform and methanol exchanged activated samples), highlighting the significant effect of activation methods on its catalytic performances. The sustainable synthetic pathway under solvent-free conditions for a broad scope of substrates using low catalyst loading and excellent recyclability made the developed pH-stable framework a promising heterogeneous catalyst.

SSZ-39 zeolite-based Ru catalysts for selective hydrogenation of levulinic acid to γ-valerolactone: Influence of synthesis method and zeolite acidity

Novel SSZ-39 zeolite-based Ru catalysts were synthesized by impregnation on as-synthesized metallic and protonated SSZ-39 and a one-pot synthesis strategy. The study focused on the influence of the SSZ-39 zeolite characteristics and catalyst preparation method type toward levulinic acid (LA) selective conversion to γ-valerolactone (GVL) under relatively mild reaction conditions (150 °C, 4 h and 2 MPa of H2 with H2O and THF as solvents). Catalysts exhibited excellent catalytic efficiency (100 % LA conversion and 98.3 % GVL selectivity) and remarkable hydrothermal stability. The results revealed a correlation between excellent catalytic activity and the structural features of the synthesized catalysts, predominantly dependent on their appropriate surface acidity (strong Lewis acid sites) and enhanced electronic interaction between Ru species and SSZ-39. The one-pot method promoted the formation of mesopores besides the zeolitic micropores present in SSZ-39; therefore, the catalyst prepared by the one-pot method (Ru/SSZ-39) showed purer SSZ-39 crystallites and a slightly larger catalytic surface area of 439 m2/g than the original zeolite surface area of 424 m2/g. In addition, the original zeolite crystals retained their morphology as spherical aggregates and remained unaffected by Ru impregnation on the metallic or protonated support during the synthesis of Ru/Na-SSZ-39 and Ru/H-SSZ-39 catalysts, respectively. Notably, it has been demonstrated that SSZ-39 zeolite effectively acts as a support for the preparation of Ru catalyst in biomass conversion reactions. Moreover, the reused catalyst exhibited consistent activity over six cycles, maintaining its structural framework without significant loss in activity.

Lewis Acidic Metal-Organic Framework Assisted Ambient Liquid Extraction Mass Spectrometry Imaging for Enhancing the Coverage of Poorly Ionizable Lipids in Brain Tissue.

The spatial distribution of lipidomes in tissues is of great importance in studies of living processes, diseases, and therapies. Mass spectrometry imaging (MSI) has become a critical technique for spatial lipidomics. However, MSI of low-abundance or poorly ionizable lipids is still challenging because of the ion suppression from high-abundance lipids. Here, a metal-organic framework (MOF) Zr6O4(OH)4(1,3,5-Tris(4-carboxyphenyl) benzene)2(triflate)6(Zr6OTf-BTB) was prepared and used for selective on-tissue adsorption of phospholipids to reduce ion suppression from them to poorly ionizable lipids. The results show that Zr6OTf-BTB with strong Lewis acidic sites and a large specific surface area (647.9 m2·g-1) could selectively adsorb phospholipids under 1% FA-MeOH. Adsorption efficiencies of phospholipids are 88.4-144.9 times higher than those of other neutral lipids. Moreover, the adsorption capacity and the adsorption kinetic rate constant of the new material to phospholipids are higher than those of Zr6-BTB (242.72 vs 73.96 mg·g-1, 0.0442 vs 0.0220 g·mg-1·min-1). A Zr6OTf-BTB sheet was prepared by a lamination technique for on-tissue phospholipid adsorption from brain tissue. Then, the tissue section on the Zr6OTf-BTB sheet was directly imaged via ambient liquid extraction-MSI with 1% FA-MeOH as the sampling solvent. The results showed that phospholipids could be 100% removed directly on tissue, and the detection coverage of the Zr6OTf-BTB-enhanced MSI method to ceramides (Cers) and hexosylceramides (HexCers) was increased by 5-26 times compared with direct tissue MSI (26 vs 1 and 17 vs 3). The new method provides an efficient and convenient way to eliminate the ion suppression from phospholipids in MSI, largely improving the detection coverage of low-abundance and poorly ionizable lipids.

Synthesis of Ethylene Carbonate by Urea Transesterification Using Zeolitic Imidazolate Framework Derived Fe-Doped ZnO Catalysts.

The development of environmentally friendly and efficient methods for the synthesis of ethylene carbonate (EC) is crucial for advancing carbon capture, utilization, and storage technologies. Herein, we present the synthesis of EC through the transesterification of urea with ethylene glycol (EG) using a zeolitic imidazolate framework (ZIF) derived Fe-doped ZnO catalyst (Fe;ZnO-ZIF). The Fe;ZnO-ZIF catalyst, prepared by incorporating Fe dopant atoms into a ZnO-ZIF template, demonstrates excellent catalytic activity, achieving high conversion of reactants and superior selectivity toward EC at 160 °C for 150 min under an applied vacuum (160 mmHg). Based on the thermogravimetric, X-ray spectroscopic, and temperature-programmed desorption analysis, the simultaneous presence of strong Lewis acidic and basic sites in Fe;ZnO-ZIF enables its excellent catalytic performance toward EC synthesis with high selectivity. Acidic sites activate the carbon center in urea, while basic sites facilitate the nucleophilic attack on urea by deprotonation of EG. This synergistic reaction pathway resulting from the interaction between the strong Lewis acidic and basic sites promotes nucleophilic attacks of EG on urea, leading to significantly higher conversion efficiency and selectivity, compared to the commercial benchmark ZnO. Although the establishment of a continuous reaction system which takes into account cyclability and stability of the catalysts is further required in the future, our research reported herein provides valuable insights into the design of synergistic, localized active sites for EC synthesis and contributes to the development of sustainable carbon utilization technologies for achievement of net-zero emissions.

Incorporation of tin into zirconium phosphate to boost efficient conversion of trioses to lactic acid

Dihydroxyacetone isomerization is a fundamental reaction for the production of lactic acid using different feedstocks. However, achieving excellent catalytic activity and resistance against leaching in water is challenging. Herein, we devised a Sn doped zirconium phosphate as effective heterogeneous catalyst. The incorporation of Sn could remarkably aggrandize the content of strong Lewis acid sites while retain relatively high surface areas. Gratifyingly, this catalyst exhibits enhanced activity and reusability for selective dihydroxyacetone isomerization into lactic acid with water as solvent. High lactic acid yields of 70.30 and 76.25% were achieved in water and water/acetone under optimal reaction conditions, respectively. The composition and activity of catalyst are reserved with reduced ions leaching. The excellent catalytic performance is attributed to accelerated conversion of pyruvaldehyde to lactic acid by the strong Lewis acid sites. Nuclear magnetic resonance revealed that the reaction is proceeded via a keto-enol tautomerization process.

Petroleum-like fuels with substantially enriched branched iso-paraffins and benzenes via boehmite-assisted pyrolysis of oil shale

Oil shale (OS) is a potential alternative to substitute/supplement traditional fossil fuels, where catalyst-assisted OS pyrolysis has become a subject of general concern. While great progresses have been realized in this field, the pursuit of high-performance catalysts for a niche OS utilization still remains a formidable challenge, because most of the catalysts face various problems, including, high cost, unsatisfactory performances, etc. Based on a two-stage flash pyrolysis, we herein report our efforts about this issue by using boehmite, a low-cost industrially relevant material of an easy availability, as catalyst. We show that boehmite could arouse 17.0 % decreases in activation energy of OS pyrolysis. When the pyrolysis is executed at the 1st stage (450 °C), the content of hydrocarbons and short-chain aliphatic hydrocarbons (≤C13), which are desired for petroleum-like fuels (PLFs), increases evidently by 56.73 % and 158.5 %, respectively, while that of heteroatomic compounds and long-chain aliphatic hydrocarbons (≥C20), which are undesired for PLFs, decreases distinctly by 60.09 % and 41.6 %, respectively, indicating an evident improvement in the quality of the pyrolysates. Fascinatingly, the content of branched iso-paraffins, especially, monomethyl-, dimethyl- and trimethyl-branched paraffins, which are either efficient octane number boosters, important tectons for functional surfactants, or significant component for high-quality fuels of excellent low-temperature performances, increases substantially by ca. 180.2 % from ca. 16.02 % to 44.89 %. For the 2nd stage at 585 °C, besides a distinctly improved quality of the pyrolysates, the content of benzene, toluene, xylene and trimethylbenzene, which are value-added chemicals broadly employed in numerous industrial fields of paramount importance, is enriched distinctly by 94 %, 65.2 %, 13 %, and 19 %, respectively. We find that the concentration of the Brönsted acid sites (BASs) of the employed boehmite, which contain 94 % medium and strong BASs, is substantially lower than that of Lewis acid sites (LASs), which contain merely 54.91 % medium and strong LASs, such that the competitive-collaborative actions of BASs and LASs confer boehmite with outstanding catalytic reactivity.

Tuning electron orbits and reducibility of spinel Co3O4 via defect engineering for enhanced acetone sensing

Defect engineering is an effective method to regulate the electronic structure and chemical properties of functional materials to improve the catalytic, electrochemical and gas-sensitive properties. However, it is still a major challenge to rationally design defects to boost the amounts and activity of reaction sites. Herein, a strategy is proposed for regulating the content of Co2+ (Oh, octahedron) and oxygen vacancies in spinel Co3O4 (Co-LDH-x, x refers to temperature) via calcination of Co layered double hydroxides (Co-LDH). Where Co2+ (Oh) serves electrons in eg orbitals with a high energy state, and rich oxygen vacancies can act as strong Lewis acid sites to generate Lewis acid-base effects with lone pair electrons. Co-LDH-700 shows excellent repeatability, stability and selectivity in acetone sensing, as well as a low detection limit of 80 ppb. The response of the sensor to 100 ppm acetone is 262.3 at 185 °C, with a rapid response rate (9.8 s). In addition, the formation of the acceptor impurity CoCo′ establishes an acceptor level above the top of the valence band, which is beneficial to the formation of thermal-induced electrons. H2-TPR confirms that the increase of Co2+ content improves the reducing capacity and catalytic effect of Co-LDH-700 in the sensing process. This work proposes a method to increase active sites by modulating Co2+ (Oh) eg orbital and rich oxygen vacancies, which provides a new idea for enhancing the activity of sensitive materials.

Enhancing catalytic ozonation activity of aluminum oxide via fluorine-doping engineering for water purification

Manipulating the electron density of active sties to develop highly efficient catalysts is expected to be one of the most ideal approaches to facilitate overall efficiency of the heterogenous catalytic ozonation (HCO) process. In this study, we demonstrate a fluorine-doping engineering to optimize the HCO activity of aluminum oxide through an improved sol–gel method using NH4F (NF-Al2O3) and HF (HF-Al2O3) as the fluorine source. We provide evidence that the fluorine atom is successfully incorporated into crystal structure of NF-Al2O3 via the formation of Al-F-Al bonds, accompany with the generation of oxygen vacancy defects, which allow for ozone molecule adsorption and activation. In contrast, the fabricated HF-Al2O3 only features the presence of AlxFy·nH2O instead of Al-F-Al structure probably due to the unexpected etching reaction. The introduction of fluorine atom largely decreases the local electron density of neighboring Al of NF-Al2O3 catalyst evidenced by the two-fold increment in the amount of strong Lewis acid sites. Consequently, the HCO activity of NF-Al2O3 catalyst is found promotion by 42.9% over pure Al2O3 in terms of the degradation kinetic rate constant (kobs). The NF-Al2O3 catalyst exhibits a powerful capacity to selectively catalyze ozone molecule into singlet oxygen (1O2), rendering the HCO system with high-tolerance to coexisting water matrixes (e.g., humic acid, chlorine ions, carbonate). Moreover, NF-Al2O3 initiated HCO system can effectively purify wastewaters from textile industry with high-quality enough to be reused for textile dyeing. Therefore, our study provides a novel strategy to develop effective HCO catalysts for promoting wastewater treatment and reuse.

Selective cracking of light cycle oil to monoaromatics over non-noble bifunctional zeolite-supported Ni and NiW catalysts

The utilization of light cycle oil (LCO) for producing monoaromatics is investigated using bifunctional Ni and NiW catalysts supported on four different zeolites at atmospheric pressure without using external H2. The order of BTX yield for various feed compositions (2-methylnaphthalene, 2-methylnaphthalene + 9-methylanthracene, LCO) is: NiW/Beta > NiW/Y > Ni/Beta > NiW/Mordenite > Ni/Y > NiW/Mix > Ni/Mordenite > Ni/Mix, whereas the coke yield exhibits the reverse trend. The better performance of NiW-based catalysts is explained by the formation of NiW oxide species and their strong interactions with the support, as ascertained through H2-TPR, XPS, and UV-DRS. The higher moderate acidity, optimal balance between medium-strength Brønsted acid sites (BAS) and strong Lewis acid sites (LAS), and the higher hydrogen transfer index (HTI) in NiW-based catalysts, facilitate the selective cracking of LCO, resulting in the desired product yield. This study also establishes a strong correlation between the structural properties of various catalysts (pore diameter, surface area, pore volume, crystallite size) and the performance parameters, thus explaining the superior performance of Beta zeolite-supported catalysts for BTX production. Experiments with NiW/Beta and a physical mixture of W/Beta and Ni/Beta show the synergistic effect due to the co-presence of Ni and W. It is inferred that triaromatics are rapidly transformed to diaromatics, and the conversion of monoaromatics having two rings determines the BTX yield. LCO compounds are found to be the primary source for the formation of monoaromatics, while n-hexadecane (n-HD) is the hydrogen source. Reaction pathways for 2-methylnaphthalene and 9-methylanthracene conversion are presented based on detailed product characterization.

Inhibiting effect of C3H6 on the performance of Cu-SSZ-13 catalysts for NH3 selective catalytic reduction

Hydrocarbons (HCs) have been found to be a potential source of catalyst poisoning in ammonia selective catalytic reduction (NH3-SCR) of NOx. As one of the predominant constituents of hydrocarbons, propene (C3H6) was selected to investigate its inhibitory effect on Cu-SSZ-13 catalysts utilized in the NH3-SCR reaction. The results of standard SCR tests mixing C3H6 and NH3 showed that the NH3-SCR activity of Cu-SSZ-13 catalysts was inhibited in the range of 150–650 °C with the introduction of C3H6 and the NOx conversion was lowest in the presence of 2000 ppm C3H6. The competitive adsorption and NH3 oxidation activity were extensively studied. It was found that NH3 and C3H6 could both be stored on Brønsted acid sites and Cu sites. The introduction of C3H6 during NH3-TPD experiments caused an increase of weakly adsorbed NH3 on the weak Lewis acid sites and a decrease of adsorbed NH3 on the strong Lewis acid sites and Brønsted acid sites, confirming the existence of the competitive adsorption between NH3 and C3H6. Based on TPO experiments, C3H6 enhanced the NH3 oxidation activities in the temperature range of 250–650 °C, and coke deposition might be generated on the catalysts, causing the decline of NOx conversion during NH3-SCR with C3H6.

Influence of sulphonation on Al-MCM-41 catalyst for effective bio-glycerol conversion to Solketal

Al-MCM-41 and sulphate modified Al-MCM-41 catalysts with variable sulphate loadings (0.25-1SAM) were synthesized through sol-gel and impregnation techniques respectively for the transformation of glycerol into solketal, a fuel additive via acetalization reaction. The mesoporous structure, surface morphologies, composition and porosity of the prepared catalysts were subjected to characterization by Low angle XRD, SEM-EDAX, TEM, FT-IR, XPS and BET-surface area studies. The strength and quantification of acid sites were obtained from TPD of NH3. Pyridine-adsorbed FTIR and 27Al MAS NMR data distinguished Lewis and Brønsted acid sites present on the catalysts. Among the synthesized catalysts, 1 N sulphated Al-MCM-41 was a better catalyst that promotes a higher solketal formation rate of 23.5 mmol h−1g cat−1 by the acetalization of glycerol. This is much higher in comparison to 4 times lesser activity of 6.1 mmol h−1gcat−1 exhibited by the parent Al-MCM-41. This catalyst further showed consistent activity and reusability up to 5 cycles. Large surface area, total acidity, strong Lewis acid sites, compatible surface characteristics of 1 N sulphated Al-MCM-41 endorse the higher acetalization activity of the catalyst. As a result, these parameters have been regarded as crucial considerations in designing a better catalyst in the effective conversion of glycerol to solketal.

Effect of metal oxides on reaction route and product distribution of catalytic cellulose hydrogenolysis

The effects of CeO2, ZrO2, Nb2O5, and ZnO catalysts supported on carbon nanotubes (CNT) relative to cellulose hydrothermal hydrogenolysis in the presence of Ni/CNT and pressured H2 was studied in this work. The catalysts were characterized by inductively coupled plasma – optical emission spectrometry, X-ray diffraction, X-ray photoelectron spectrometry, transmission electron microscopy, NH3 temperature programmed desorption (TPD), and CO2-TPD. Glucose and its isomers were detected by mass spectrometry. The results showed that redox active CeO2/CNT with strong Lewis acid and strong Lewis base sites was active in C-C bong cracking, isomerization, dehydrogenation, and hydrodeoxygenation reaction, yielding 36.3% ethylene glycol and 17.2% 1,2-propylene glycol. The ZnO/CNT with Bronsted base accelerated isomerization, retro-aldol condensation, and dehydrogenation, yielding 20.7% 1,2-propylene glycol, 17.8% ethylene glycol, and 12.7% tetrahydrofuran dimethanol. The Nb2O5/CNT and ZrO2/CNT were inert to C-C bond cracking, whereas H+ in hot compressed water and the Bronsted acid in Nb2O5/CNT accelerated dehydration, yielding more sorbitol and sorbitans. The results provide reference for catalyst selection and product regulation in cellulose hydrogenolysis.

Distinguishing the roles of anatase TiO2 nanocrystals with {101}, {010} or {001} facets catalyzed O3/H2O2 for low-temperature NO oxidation

To study the crystal facets effects of TiO2 on catalytic O3/H2O2 for NO oxidation at low temperature, anatase TiO2 nanocrystals with a high percentage of {101}, {010} and {001} facets were prepared by hydrothermal routes without fluorine. The percentages of the {101}, {010} and {001} facets in these three samples were 80%, 70% and 66%, respectively. The sequence of NO oxidation efficiency was determined as TiO2(001) (92%) > TiO2(101) (86%) > TiO2(010) (71%) under the molar ratio of O3/NO = 0.5 and H2O2/NO = 2.9. The crystal facets mechanism exhibited that TiO2(010) sample had the strongest Lewis acid sites, but TiO2(010) activated H2O2 to produce a stable Ti-OOH, which could not react with O3 to generate more •O2– radicals. TiO2(101) possessed a lower density of five-coordinated Ti atoms (Ti5c) than TiO2(010) and TiO2(001), the cooperative effect between Ti5c and H2O2 was the weakest. On the contrary, Ti-OOH on the surface of TiO2(001) was more active for •O2– production, meanwhile, TiO2(001) also exhibited the strongest NO adsorption properties. Thus, TiO2(001) had excellent NO oxidation efficiency.