介孔磷酸铌一锅法高效催化木糖制备糠醛

木糖转化到糠醛一般包括两步: 首先在酶、碱或路易斯(L)酸的催化作用下异构化木糖到木酮糖, 接下来木酮糖在酸的作用下脱水得到糠醛. 针对木糖水相脱水一步制备糠醛, 利用十六烷基三甲基溴化铵(CTAB)为模板剂, 借助软模板合作策略制备了一种抗水的新型固体酸催化剂, 介孔磷酸铌, 并利用X射线衍射(XRD)、N₂吸脱附、透射电镜(TEM)、氨气程序升温脱附(NH₃-TPD)和吡啶吸附傅里叶变换红外(Py-FTIR)光谱对材料的结构和酸性质进行了表征. 研究发现介孔磷酸铌不仅具有很高的比表面积(>200 m²·g^-1), 比较窄的孔径分布(3.5nm), 同时还具有很强的L酸性和布朗斯特(B)酸性. 通过L酸催化的木糖异构化为木酮糖/来苏糖和B酸催化的木酮糖/来苏糖进一步脱水得到糠醛, 实现了一步由木糖到糠醛的高效转化. 为了优化反应条件, 考察了水溶液中反应温度、投料质量比及反应时间对木糖转化率和糠醛收率的影响, 在最佳的反应条件下, 木糖的转化率为96.5%, 糠醛的收率达49.8%. 进一步地, 为了提高收率且易于分离, 利用4-甲基-2-戊酮(MIBK)/NaCl水溶液(体积比为7:3)作为反应混合溶剂, 使糠醛收率提高到68.4%.     

Catalytic Conversion of Xylose to Furfural by p-Toluenesulfonic Acid (pTSA) and Chlorides: Process Optimization and Kinetic Modeling

Furfural is one of the most promising precursor chemicals with an extended range of downstream derivatives. In this work, conversion of xylose to produce furfural was performed by employing p-toluenesulfonic acid (pTSA) as a catalyst in DMSO medium at moderate temperature and atmospheric pressure. The production process was optimized based on kinetic modeling of xylose conversion to furfural alongwith simultaneous formation of humin from xylose and furfural. The synergetic effects of organic acids and Lewis acids were investigated. Results showed that the catalyst pTSA-CrCl₃·6H₂O was a promising combined catalyst due to the high furfural yield (53.10%) at a moderate temperature of 120 °C. Observed kinetic modeling illustrated that the condensation of furfural in the DMSO solvent medium actually could be neglected. The established model was found to be satisfactory and could be well applied for process simulation and optimization with adequate accuracy. The estimated values of activation energies for xylose dehydration, condensation of xylose, and furfural to humin were 81.80, 66.50, and 93.02 kJ/mol, respectively.     

AlCl3催化玉米秸秆中半纤维素的选择性转化

研究了AlCl₃ 催化剂作用下, 水热体系中玉米秸秆中半纤维素组分在温和条件下的选择性转化. 详细考察了反应温度、反应时间和AlCl₃用量对半纤维素选择性转化的影响. 原料及反应后的固体残渣分别采用化学滴定、X射线衍射和扫描电镜进行表征. 结果表明, 140 ℃下反应1 h可转化玉米秸秆中的大部分半纤维素, 转化率为85.1%;而玉米秸秆中的绝大部分纤维素和木质素组分仍保留在固体残渣中, 此时纤维素和木质素的转化率分别为10.7%和23.9%. 半纤维素转化的主要液体产物为木糖, 同时含有一些乙酸和糠醛. 升高温度, 将滤液进行进一步反应可促进木糖的转化. 在水/四氢呋喃反应体系中, 滤液的进一步反应有利于乙酰丙酸、甲酸和糠醛的生成. 固体酸催化剂γ-Al₂O₃/SO₄^2-的加入可进一步提高糠醛的收率.     

The Optimization of Dilute Acid Hydrolysis of Cotton Stalk in Xylose Production

Cotton stalk, a lignocellulosic waste material, is composed of xylose that can be used as a raw material for production of xylitol, a high-value product. There is a growing interest in the use of lignocellulosic wastes for conversion into various chemicals because of their low cost and the fact that they are renewable and abundant. The objective of the study was to determine the effects of H₂SO₄ concentration, temperature, and reaction time on the production of sugars (xylose, glucose, and arabinose) and on the reaction by-products (furfural and acetic acid). Response surface methodology was used to optimize the hydrolysis process in order to obtain high xylose yield and selectivity. The optimum reaction temperature, reaction time, and acid concentration were 140 °C, 15 min, and 6%, respectively. Under these conditions, xylose yield and selectivity were found to be 47.88% and 2.26 g g⁻¹, respectively.     

Selective conversion of cellulose to levulinic acid and furfural in sulfolane/water solvent

Direct conversion of cellulose into levulinic acid and furfural in sulfolane media with the aid of water and H₂SO₄ was performed at 140–220 °C under the pressures of 0–1.5 MPa. This approach could obtain 72.5 mol% levulinic acid and 11.5 mol% furfural formation under an optimal condition in which the mass ratio of sulfolane, water and H₂SO₄ was 90:10:1. It was found that the decrease of water content led to an increasing yield of furfural and that the maximum furfural yield (51.1 mol%) could be obtained in the absence of water. The synergism of sulfolane and water in the selective liquefied system was demonstrated to be responsible for not only reinforced effect of optimizing and isolating the target products but also for reducing re-polymerization and side reactions. Furthermore, sulfolane in our case could be recycled and re-used for the conversion of cellulose with the same yield, which shed light on the remarkable potential for future industrial application.     

用Lewis酸或Brnsted酸催化剂和N2汽提法使木糖脱水为糠醛（英文）

The activity of Lewis (Nb2O5) and Br nsted (Amberlyst 70) acid catalysts for the cyclodehydration of xylose to furfural was studied. The nature of the acidity resulted in significant changes in the reaction mechanism. Lewis acid sites promote the formation of xylulose, while Br nsted acid sites are required to further dehydrate the sugar to furfural. Amberlyst 70 in water/toluene at 175 ℃ showed lower activity but gave a higher furfural yield. Using N2 as the stripping agent considerably improved the furfural yield and product purity in the stripped stream. Catalyst stability was also studied.     

二个钴5-磺酸基水杨酸、邻菲罗啉配合物的合成、次级合成与结构

Cobait（Ⅱ） nitrate reacted with 1,10-phenanthroline （phen） and 5-sulfosaiicylic acid （H3ssal） to yield the cobait（Ⅰ） complex [Co（phen）2（H2O）2]（Hssal）o4H2O （1） and the reaction of 1 with copper acetate led to a novel complex [Co（phen）（H2O）4][Cu2（ssal）2（phen）2]·5H2O （2）. These two complexes were cationanion species and the cationic motif [Co（phen）2（H2O）2]^2＋of 1 could be converted to [Co（phen）（H2O）4]^2＋ in the formation process of new anion [Cu2（phen）2（ssal）2]^2- of 2. In both complexes abundant hydrogen bonds construct different supramolecular architectures, thus the conversion reaction can provide a new path to create novel supramolecular network.     

Electrochemical Hydroxylation of Arenes Catalyzed by a Keggin Polyoxometalate with a Cobalt(IV) Heteroatom

The sustainable, selective direct hydroxylation of arenes, such as benzene to phenol, is an important research challenge. An electrocatalytic transformation using formic acid to oxidize benzene and its halogenated derivatives to selectively yield aryl formates, which are easily hydrolyzed by water to yield the corresponding phenols, is presented. The formylation reaction occurs on a Pt anode in the presence of [Co^IIIW₁₂O₄₀]^5? as a catalyst and lithium formate as an electrolyte via formation of a formyloxyl radical as the reactive species, which was trapped by a BMPO spin trap and identified by EPR. Hydrogen was formed at the Pt cathode. The sum transformation is ArH+H₂O→ArOH+H₂. Non‐optimized reaction conditions showed a Faradaic efficiency of 75 % and selective formation of the mono‐oxidized product in a 35 % yield. Decomposition of formic acid into CO₂ and H₂ is a side‐reaction.     

Humins with Efficient Electromagnetic Wave Absorption: A By-Product of Furfural Conversion to Isopropyl Levulinate via a Tandem Catalytic Reaction in One-Pot

Both one-pot catalytic conversion of furfural (FAL) to isopropyl levulinate (PL) and carbonization of by-product (humins) for electromagnetic wave absorption are discussed, which provides inspiration that humins can be applied to electromagnetic wave absorption. In the former, phosphotungstic acid (PW) is employed as a homogeneous catalyst to convert FAL to PL via a tandem reaction in one pot, with the formation of a vast amount of humins. With FAL and various intermediates as substrates, it was found that humins was a polymerization product of FAL, furfuryl alcohol (FOL) and furfuryl ester (FE) with furan rings. In addition, the in situ attenuated total reflection infrared (ATR-IR) spectra also provided a basis for the proposed reaction route. In the latter, with the humins as raw material, P species and WO₃ doped nano-porous carbon (Humins-700) platform formed after high-temperature annealing is used for electromagnetic wave absorption and manifests desirable absorption performance. The minimum reflection loss (RL_min) value is −47.3 dB at 13.0 GHz with a thickness of 2.0 mm and the effective absorption bandwidth reaches 4.5 GHz (11.2–5.7 GHz).     

H+−H− Pairs in Partially Oxidized MAX Phases for Bifunctional Catalytic Conversion of Furfurals into Linear Ketones

Currently, less favorable C=O hydrogenation and weak concerted acid catalysis cause unsatisfactory catalytic performance in the upgrading of biomass-derived furfurals (i.e., furfural, 5-methyl furfural, and 5-hydroxymethyl furfural) to ketones (i.e., cyclopentanone, 2,5-hexanedione, and 1-hydroxyl-2,5-hexanedione). A series of partially oxidized MAX phase (i.e., Ti₃AlC₂, Ti₂AlC, Ti₃SiC₂) supporting Pd catalysts were fabricated, which showed high catalytic activity; Pd/Ti₃AlC₂ in particular displayed high performance for conversion of furfurals into targeted ketones. Detailed studies of the catalytic mechanism confirm that in situ hydrogen spillover generates Frustrated Lewis H⁺−H⁻ pairs, which not only act as the hydrogenation sites for selective C=O hydrogenation but also provide acid sites for ring opening. The close intimate hydrogenation and acid sites promote bifunctional catalytic reactions, substantially reducing the reported minimum reaction temperature of various furfurals by at least 30–60 °C.     

Conversion factors for carbohydrate analysis by hydrolysis and <Superscript>1</Superscript>H-NMR spectroscopy

Conversion factor to calibrate the lower xylan content in carbohydrate compositional analysis in wood by ¹H-NMR spectroscopy was investigated. During acid hydrolysis, xylan monomer was dehydrated as furfural, and that furfural was further degraded or condensed in acidic reaction condition. Anomeric hydrogen peaks integration in ¹H-NMR spectroscopic method excluded xylose reacted products (such as furfural and their condensed or degraded products). Only 52% of xylose was counted in anomeric hydrogen integration and 62% of xylose was counted in integration of furfural peak and anomeric hydrogen. For accurate carbohydrate compositional analysis by NMR spectroscopic method, furfural and their reacted products should be counted as xylose. Conversion factor for xylose content analysis was introduced from the acid hydrolysis of several different combinations of standard cellulose and xylan. In this study xylan conversion factor 0.66 was obtained based on compared NMR data from the prepared cellulose and xylan mixtures acid hydrolyzed with the same condition for woodmeal and pulps. With corrected xylan content calculation, NMR spectroscopic method gave rather closer carbohydrate composition compared to the other analytical methods.     

Ionothermal Synthesis of a NaCl‐type Topological Network Based on Trinuclear Cobalt(II) Clusters as Nodes

A new metal‐organic network [Co₃(tbip)₃(H₂O)₄] · 2H₂O ( 1 ) (H₂tbip = 5‐tert‐butyl‐isophthalic acid) was synthesized through the ionothermal reaction of H₂tbip, cobalt nitrate, and [bmim]Br ionic liquid ([bmim]Br = 1‐butyl‐3‐methylimidazolium bromide). It exhibits a three‐dimensional (3D) framework with NaCl topology based on trinuclear cobalt(II) clusters as nodes. The magnetic studies show that there exist antiferromagnetic interactions between the Co^II ions.     

Effects of mixed aqueous‐organic solvents on the rate of intramolecular carboxylic group‐catalyzed cleavage of N‐(4′‐methoxyphenyl)phthalamic acid

Kinetic study on the cleavage of N‐(4′‐methoxyphenyl)phthalamic acid (NMPPAH) in mixed H₂O‐CH₃CN and H₂O‐1,4‐dioxan solvents containing 0.05 M HCl reveals the formation of phthalic anhydride (PAn)/phthalic acid (PA) as the sole or major product. Pseudo first‐order rate constants (k₁) for the conversion of NMPPAH to PAn decrease nonlinearly from 60.4 × 10^?5 to 2.64 × 10^?5 s^?1 with the increase in the contents of 1,4‐dioxan from 10 to 80% v/v in mixed aqueous solvents. The rate of cleavage of NMPPAH in mixed H₂O‐CH₃CN solvents at ≥50% v/v CH₃CN follows an irreversible consecutive reaction path: NMPPAH PA. The values of k₁ are larger in H₂O‐CH₃CN than in H₂O‐1,4‐dioxan solvents. © 2004 Wiley Periodicals, Inc. Int J Chem Kinet 36: 316–325, 2004     

Optimizing Dilute-Acid Pretreatment of Rapeseed Straw for Extraction of Hemicellulose

Biological conversion of biomass into fuels and chemicals requires hydrolysis of the polysaccharide fraction into monomeric sugars prior to fermentation. Hydrolysis can be performed enzymatically or with mineral acids. In this study, dilute sulfuric acid was used as a catalyst for the pretreatment of rapeseed straw. The purpose of this study is to optimize the pretreatment process in a 15-mL bomb tube reactor and investigate the effects of the acid concentration, temperature, and reaction time. These parameters influence hemicellulose removal and production of sugars (xylose, glucose, and arabinose) in the hydrolyzate as well as the formation of by-products (furfural, 5-hydroxymethylfurfural, and acetic acid). Statistical analysis was based on a model composition corresponding to a 3³ orthogonal factorial design and employed the response surface methodology to optimize the pretreatment conditions, aiming to attain maximum xylan, mannan, and galactan (XMG) extraction from hemicellulose of rapeseed straw. The obtained optimum conditions were: H₂SO₄ concentration of 1.76% and temperature of 152.6 °C with a reaction time of 21 min. Under these optimal conditions, 85.5% of the total sugar was recovered after acid hydrolysis (78.9% XMG and 6.6% glucan). The hydrolyzate contained 1.60 g/L glucose, 0.61 g/L arabinose, 10.49 g/L xylose, mannose, and galactose, 0.39 g/L cellobiose, 0.94 g/L fructose, 0.02 g/L 1,6-anhydro-glucose, 1.17 g/L formic acid, 2.94 g/L acetic acid, 0.04 g/L levulinic acid, 0.04 g/L 5-hydroxymethylfurfural, and 0.98 g/L furfural.     

Formic acid catalyzed gas-phase reaction of H2O with SO3 and the reverse reaction: a theoretical study

The formic acid catalyzed gas‐phase reaction between H₂O and SO₃ and its reverse reaction are respectively investigated by means of quantum chemical calculations at the CCSD(T)//B3LYP/cc‐pv(T+d)z and CCSD(T)//MP2/aug‐cc‐pv(T+d)z levels of theory. Remarkably, the activation energy relative to the reactants for the reaction of H₂O with SO₃ is lowered through formic acid catalysis from 15.97 kcal mol^?1 to ?15.12 and ?14.83 kcal mol^?1 for the formed H₂O ??? SO₃ complex plus HCOOH and the formed H₂O ??? HCOOH complex plus SO₃, respectively, at the CCSD(T)//MP2/aug‐cc‐pv(T+d)z level. For the reverse reaction, the energy barrier for decomposition of sulfuric acid is reduced to ?3.07 kcal mol^?1 from 35.82 kcal mol^?1 with the aid of formic acid. The results show that formic acid plays a strong catalytic role in facilitating the formation and decomposition of sulfuric acid. The rate constant of the SO₃+H₂O reaction with formic acid is 10⁵ times greater than that of the corresponding reaction with water dimer. The calculated rate constant for the HCOOH+H₂SO₄ reaction is about 10^?13 cm³ molecule^?1 s^?1 in the temperature range 200–280 K. The results of the present investigation show that formic acid plays a crucial role in the cycle between SO₃ and H₂SO₄ in atmospheric chemistry.     

Palladium‐Catalyzed Aerobic Intermolecular Cyclization of Acrylic Acid with 1‐Octene to Afford α‐Methylene‐γ‐butyrolactones: The Remarkable Effect of Continuous Water Removal from the Reaction Mixture and Analysis of the Reaction by Kinetic,ESI‐MS,and XAFS Measurements

Further study of our aerobic intermolecular cyclization of acrylic acid with 1‐octene to afford α‐methylene‐γ‐butyrolactones, catalyzed by the Pd(OCOCF₃)₂/Cu(OAc)₂ ? H₂O system, has clarified that the accumulation of water generated from oxygen during the reaction causes deactivation of the Cu cocatalyst. This prevents regeneration of the active Pd catalyst and, thus, has a harmful influence on the progress of the cyclization. As a result, both the substrate conversion and product yield are efficiently improved by continuous removal of water from the reaction mixture. Detailed analysis of the kinetic and spectroscopic measurements performed under the condition of continuous water removal demonstrates that the cyclization proceeds in four steps: 1) equilibrium coordination of 1‐octene to the Pd acrylate species, 2) Markovnikov‐type acryloxy palladation of 1‐octene (1,2‐addition), 3) intramolecular carbopalladation, and 4) β‐hydride elimination. Byproduct 2‐acryloxy‐1‐octene is formed by β‐hydride elimination after step 2). These cyclization steps fit the Michaelis–Menten equation well and β‐hydride elimination is considered to be a rate‐limiting step in the formation of the products. Spectroscopic data agree sufficiently with the existence of the intermediates bearing acrylate (Pd? O bond), η³‐C₈H₁₅ (Pd? C bond), or C₁₁H₁₉O₂ (Pd? C bond) moieties on the Pd center as the resting‐state compounds. Furthermore, not only Cu^II, but also Cu^I, species are observed during the reaction time of 2–8 h when the reaction proceeds efficiently. This result suggests that the Cu^II species is partially reduced to the Cu^I species when the active Pd catalytic species are regenerated.     

Production of Xylose from Meranti Wood Sawdust by Dilute Acid Hydrolysis

Xylitol production by bioconversion of xylose can be economically interesting if the raw material can be recovered from a cheap lignocellulosic biomass (LCB). Meranti wood sawdust (MWS) is a renewable and low-cost LCB that can be used as a promising and economic source of xylose, a starting raw material for the manufacture of several specialty chemicals, especially xylitol. This study aimed to optimize the hydrolysis process of MWS and to determine the influence of temperature, H₂SO₄ concentration, and residence time on xylose release and on by-product formation (glucose, arabinose, acetic acid, furfural, hydroxymethylfurfural (HMF), and lignin degradation products (LDPs)). Batch hydrolysis was conducted under various operating conditions, and response surface methodology was adopted to achieve the highest xylose yield. Xylose production was highly affected by temperature, acid concentration, and residence time. The optimum temperature, acid concentration, and time were determined to be 124 °C, 3.26 %, and 80 min, respectively. Under these optimum conditions, xylose yield and selectivity were attained at 90.6 % and 4.05 g/g, respectively.     

Exploring Regioselective Bond Cleavage and Cross‐Coupling Reactions using a Low‐Valent Nickel Complex

Recently, esters have received much attention as transmetalation partners for cross‐coupling reactions. Herein, we report a systematic study of the reactivity of a series of esters and thioesters with [{(dtbpe)Ni}₂(μ‐η²:η²‐C₆H₆)] (dtbpe=1,2‐bis(di‐tert‐butyl)phosphinoethane), which is a source of (dtbpe)nickel(0). Trifluoromethylthioesters were found to form η²‐carbonyl complexes. In contrast, acetylthioesters underwent rapid C_acyl?S bond cleavage followed by decarbonylation to generate methylnickel complexes. This decarbonylation could be pushed backwards by the addition of CO, allowing for regeneration of the thioester. Most of the thioester complexes were found to undergo stoichiometric cross‐coupling with phenylboronic acid to yield sulfides. While ethyl trifluoroacetate was also found to form an η²‐carbonyl complex, phenyl esters were found to predominantly undergo C_aryl?O bond cleavage to yield arylnickel complexes. These could also undergo transmetalation to yield biaryls. Attempts to render the reactions catalytic were hindered by ligand scrambling to yield nickel bis(acetate) complexes, the formation of which was supported by independent syntheses. Finally, 2‐naphthyl acetate was also found to undergo clean C_aryl?O bond cleavage, and although stoichiometric cross‐coupling with phenylboronic acid proceeded with good yield, catalytic turnover has so far proven elusive.     

糠醛在Pt(111)表面的吸附和脱碳反应

采用广义梯度近似的密度泛函理论并结合平板模型的方法, 优化了糠醛分子在Pt(111)面的吸附模型,并探究了糠醛脱碳反应形成呋喃的机理. 结果表明: 吸附后糠醛分子环上的C―H(O)键及支链―CHO相对于金属表面倾斜上翘, 分子平面被扭曲, 易于呋喃的形成; 同时, 糠醛分子向Pt表面转移电子0.765e, 环中的大π键与Pt(111)表面的d轨道发生较强的相互作用, 使得糠醛的芳香性被破坏, 环上的碳原子呈现准sp³杂化. 此外, 对糠醛脱碳反应中的各反应步骤进行过渡态搜索, 通过比较各步骤的活化能, 得出糠醛更易先失去支链上的H形成酰基中间体(C₄H₃O)CO, 中间体继续脱碳加氢形成产物呋喃. 该过程的控速步骤为(C₄H₃O)CO^*+^*→C₄H₃O^*+CO^* (^*为吸附位),活化能为127.65 kJ·mol^-1.     

An Unexplored O2‐Involved Pathway for the Decarboxylation of Saturated Carboxylic Acids by TiO2 Photocatalysis: An Isotopic Probe Study

The aerobic decarboxylation of saturated carboxylic acids (from C₂ to C₅) in water by TiO₂ photocatalysis was systematically investigated in this work. It was found that the split of C¹? C² bond of the acids to release CO₂ proceeds sequentially (that is, a C₅ acid sequentially forms C₄ products, then C₃ and so forth). As a model reaction, the decarboxylation of propionic acid to produce acetic acid was tracked by using isotopic‐labeled H₂¹⁸O. As much as ≈42 % of oxygen atoms of the produced acetic acids were from dioxygen (¹⁶O₂). Through diffuse reflectance FTIR measurements (DRIFTS), we confirmed that an intermediate pyruvic acid was generated prior to the cut‐off of the initial carboxyl group; this intermediate was evidenced by the appearance of an absorption peak at 1772 cm^?1 (attributed to C?O stretch of α‐keto group of pyruvic acid) and the shift of this peak to 1726 cm^?1 when H₂¹⁶O was replaced by H₂¹⁸O. Consequently, pyruvic acid was chosen as another model molecule to observe how its decarboxylation occurs in H₂¹⁶O under an atmosphere of ¹⁸O₂. With the α‐keto oxygen of pyruvic acid preserved in the carboxyl group of acetic acid, ≈24 % new oxygen atoms of the produced acetic acid were from molecular oxygen at near 100 % conversion of pyruvic acid. The other ≈76 % oxygen atoms were provided by H₂O through hole/OH radical oxidation. In the presence of conduction band electrons, O₂ can independently accomplish such C¹? C² bond cleavage of pyruvic acid to generate acetic acid with ≈100 % selectivity, as confirmed by an electrochemical experiment carried out in the dark. More importantly, the ratio of O₂ participation in decarboxylation increased along with the increase of pyruvic acid conversion, indicating the differences between non‐substituted acids and α‐keto acids. This also suggests that the O₂‐dependent decarboxylation competes with hole/OH‐radical‐promoted decarboxylation and depends on TiO₂ surface defects at which Ti_4c sites are available for the simultaneous coordination of substrates and O₂.