Effect of MgO calcination temperature on the reaction products and kinetics of MgO–SiO2–H2O system

MgO-based binders have been widely studied for decades. Recently, the MgO–SiO₂–H₂O system was developed as a novel construction material, however, its reaction mechanism remains unclear. This paper investigated the reaction products and kinetics of MgO/silica fume (SF) pastes with MgO calcinated at different temperatures. The results indicate that MgO presented larger grain size after calcination at higher temperature. Mg(OH)₂ and magnesium silicate hydrate (M–S–H) gel were formed when using MgO calcined at 850, 950, and 1050°C. However, only M–S–H gel was formed when using MgO calcined at 1450°C. The reaction kinetics of MgO could be described using α = 1 − e^−k*t. The reaction rate of MgO increased with decreasing calcination temperature, increasing SF dosage, and the addition of sodium hexametaphosphate. Only M–S–H gel was formed when the reaction rate of MgO was below the demarcation line (about 0.250 × 10⁻⁶ s⁻¹), and the corresponding demarcation area was around 14 days.     

Catalytic Hydrocracking of a Bitumen‐Derived Asphaltene over NiMo/γ‐Al2O3 at Various Temperatures

Hydrocracking of a bitumen‐derived asphaltene over NiMo/γ‐Al₂O₃ was investigated in a microbatch reactor at varying temperatures. The molar kinetics of asphaltene cracking reaction was examined by fitting the experimental data. Below a defined temperature, the molar reaction showed the first‐order kinetic feature while at higher temperatures secondary reactions such as coke formation became significant, causing deviation of the reaction behavior from the proposed first‐order kinetic model. Selectivity analysis proved that dominant products varied from gases to liquids to gases with increasing temperature, shifting the dominant reaction from C–S bonds cleavage to C–C bonds cleavage.     

Synthesis and Characterization of Phosphonates from Methyl Linoleate and Vegetable Oils

Phosphonates were synthesized on a medium scale (~200 g) from three lipids—methyl linoleate (MeLin), high‐oleic sunflower oil (HOSO) and soybean oil (SBO), and three dialkyl phosphites—methyl, ethyl and n‐butyl, using a radical initiator. A staged addition of the lipid and the initiator was used to achieve good yields. Good results were observed with MeLin (94–99% conversions of the double bonds, as determined by NMR, and 83–99% isolated yields) and HOSO (99–100% NMR conversions, 87–96% isolated yields) using tert‐butyl perbenzoate as the initiator. With SBO, benzoyl peroxide was used as the initiator, due to its capability to generate radicals at a higher rate at slightly lower temperatures, and thus to shorten the reaction time. Conversions of 91–93% (by NMR) and isolated yields of 80–94% were achieved. The progress of the reaction was monitored with GC–MS. The products were characterized using ¹H, ¹³C and ³¹P NMR, IR and gel permeation chromatography. A prolonged reaction led to some transesterification between the carboxylic and phosphite ester groups. Conditions favoring higher reaction rates led to the formation of more oligomers and benzoate fatty ester byproducts. The benzoate fatty ester byproducts were formed by the attack of a benzoate radical on a double bond. The more double bonds that were present per lipid molecule, the more oligomers were formed: MeLin 2–8%, HOSO 3–9% and SBO 8–29%.     

Decomposition of Ethanol Over Ru(0001): A DFT Study

We studied decomposition pathways of ethanol on Ru(0001) with periodic slab-model calculations using a DFT-GGA approach. We calculated the adsorption modes of ethanol and several of its dehydrogenation products and we evaluated reaction energies as well as activation barriers of pertinent dehydrogenation, C–C, and C–O cleavage steps. The calculated barrier heights of C–C and C–O scission steps can be related to the number of hydrogen atoms bound to the C1–C2 and C1–O moieties of the intermediates, respectively. Two counteracting effects are at work, increasing with each dehydrogenation: (i) higher order of the pertinent bond of the adsorbate, and (ii) stronger substrate-surface interaction and thus better stabilization of the transition state. For most intermediates we determined C–O cleavage to be both kinetically and thermodynamically favored over C–C scission, except for the highly dehydrogenated species CH _k CO (k = 1, 2). Based on the calculated energetics, the most likely decomposition pathway, with a rate-determining barrier at 77 kJ·mol^?1, leads to the formation of ketene CH₂CO and subsequent C–C cleavage yielding methylene and CO.     

Transition metal catalyzed oxidations. 13

The secondary N-aryl-N-alkyl amines 1 – 3 and 5 are oxidized by the Zr(O-t-Bu)₄/TBHP system to nitrobenzene ( 6 ) and the corresponding carbonyl compounds with cleavage of the C–N bond. Nitrones are postulated as reaction intermediates as demonstrated by the cleavage of 9 – 11 to nitrobenzene ( 6 ) and the benzaldehydes 12 – 14 by the same catalytic oxidation system.     

Reaction mechanism and kinetics for hydrolytic dehydrogenation of ammonia borane on a Pt/CNT catalyst

A reaction mechanism is proposed for hydrolytic dehydrogenation of ammonia borane on a Pt/CNT catalyst. A combination of thermodynamic analysis and FTIR measurement reveals that B‐containing byproducts are mainly in the form of an NH₄B(OH)₄‐B(OH)₃ mixture rather than NH₄BO₂ reported previously. The revised main reaction is , involving the B–H, B–N, and O–H bond cleavages. Isotopic experiments using D₂O instead of H₂O as reactant or introducing D₂ into the reaction atmosphere suggest the O–H bond cleavage being in the rate‐determining step, and an unfavorable occurrence of the chemisorbed H₂O dissociation (i.e., the direct O–H bond cleavage), respectively. Different reaction pathways with indirect O–H bond cleavages are analyzed, and then is suggested as the rate‐determining step. Subsequently, a Langmuir–Hinshelwood kinetic model is developed, which fits well with the experimental data. © 2016 American Institute of Chemical Engineers AIChE J, 63: 60–65, 2017     

Aqueous Phase Glycerol Reforming with Pt and PtMo Bimetallic Nanoparticle Catalysts: The Role of the Mo Promoter

The turnover rate (TOR, normalized to sites measured by CO chemisorption before reaction) and selectivity for the aqueous phase reforming of glycerol have been determined for Pt/C and PtMo/C catalysts. While the TOR of PtMo/C is higher than that of Pt/C by about 4 times at comparable conversion, the selectivity to C–O bond cleavage is higher, thus reducing the H₂ yield at high conversion. Under reaction conditions on Pt/C, CO is observed as the most abundant Pt surface species with a fractional coverage of about 0.6 using operando X-ray absorption spectroscopy. Since there is little CO in the effluent (CO₂:CO ratios > 100:1, when CO is detected), it is thought that surface CO is converted to H₂ and CO₂ by the water gas shift reaction. DFT calculations suggest that the role of metallic Mo is to alter the electronic properties of Pt lowering the binding energy of CO and reducing the activation energies of dehydrogenation and C–O bond cleavage. Because the activation energy for C–O cleavage is lowered more than for dehydrogenation, the selectivity for C–O bond cleavage is increased, ultimately lowering the H₂ yield compared to Pt/C.     

The catalytic activity of the Pr2Zr2−xFexO7±δ system for the CO oxidation reaction

One of the alternatives to decrease the concentration of CO is its oxidation reaction to CO₂, which can be made more efficient using catalysts. In this work, it is shown that pyrochlore structures are a promising candidate to act as heterogeneous catalysts due to their chemical and physical properties. For use as a catalyst in this reaction, the Pr₂Zr_2−xFe_xO_7±δ (x = 0, 0.05, 0.10, and 0.15) system was synthesized by the solvothermal method, firing the powder obtained at temperatures of 1200 and 1400°C. The diffraction patterns confirmed the pyrochlore structure as the single phase in all the nominal compositions. The Brunauer–Emmett–Teller method and dynamic light-scattering analysis showed an increase in the particle size and a decrease in the specific surface area when increasing the iron concentration and increasing the calcination temperature. The compositions that presented the best catalytic activity were the samples with the highest iron concentration. Moreover, these samples were able to convert all the CO oxidation reactions in a narrower temperature range than a conventional CeO₂ sample. The presence of vacancies and the redox behavior of the elements present are the key factors for the catalysis of this system in the CO oxidation reaction.     

Synthesis of functionalized liquid rubbers from polyisoprene

Noncatalytic transformation of cis‐1,4‐polyisoprene rubber (M_n = 320,000) into functionalized liquid rubbers containing various amounts of carbonyl groups was studied. The process is performed via selective carboxidation of the polymer C?C bonds by nitrous oxide (N₂O) in the temperature range of 180–230°C and under 3–6 MPa pressure. The carboxidation proceeds by the nonradical type mechanism involving the 1,3‐dipolar cycloaddition of N₂O to the C?C bond. The main route of the reaction (ca. 65%) proceeds without cleavage of the internal C?C bonds and leads to the formation of ketone groups in the polymer backbone. The second route (ca. 35%) includes the cleavage of C?C bonds, yielding the molecules of a smaller size. This route results in a manifold decrease of the molecular weight, which, depending on the carboxidation degree, may be more than two orders of magnitude less than that of the parent rubber. A series of functionalized liquid rubbers having M_n value from 1000 to 19,000, and the oxygen content from 0.3 to 3.9 wt % was obtained in the form of the liquid unsaturated polyketones. Similar polyketones can also be prepared by carboxidation of the natural rubber. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Catalytic Scope of the Thiamine‐Dependent Multifunctional Enzyme Cyclohexane‐1,2‐dione Hydrolase

The thiamine diphosphate (ThDP)‐dependent enzyme cyclohexane‐1,2‐dione hydrolase (CDH) was expressed in Escherichia coli and purified by affinity chromatography (Ni‐NTA). Recombinant CDH showed the same C?C bond‐cleavage and C?C bond‐formation activities as the native enzyme. Furthermore, we have shown that CDH catalyzes the asymmetric cross‐benzoin reaction of aromatic aldehydes and (decarboxylated) pyruvate (up to quantitative conversion, 92–99 % ee). CDH accepts also hydroxybenzaldehydes and nitrobenzaldehydes; these previously have not (or only in rare cases) been known as substrates of other ThDP‐dependent enzymes. On a semipreparative scale, sterically demanding 4‐(tert‐butyl)benzaldehyde and 2‐naphthaldehyde were transformed into the corresponding 2‐hydroxy ketone products in high yields. Additionally, certain benzaldehydes with electron withdrawing substituents were identified as potential inhibitors of the ligase activity of CDH.     

Synthesis of polyglutarimides from p(methyl methacrylate) and cyclohexylamine. I. Influence of working conditions on imidization reaction

Over the last 50 years methacrylic polymers, especially poly(methyl methacrylate) (PMMA), have reached a noteworthy place in world polymer production. However, for special applications that require thermal properties, polycarbonates take the place of PMMA because of the latter's low glass transition temperature (T_g) of 105°C. The aminolysis reaction of PMMA with cyclohexylamine in xylene was studied to obtain a polyglutarimide exhibiting higher T_g values. The mechanism involving aminolysis and further amidization of ester groups was correlated with the experimental characterization of all the species created during the reaction. Poly(N‐cyclohexylacrylamide) and polyglutarimide (prepared from this precursor) were prepared in order to determine the special characteristics of these model compounds by FTIR. This method abled the quantification of ester, amide, acid, and imide groups. This aminolysis reaction was optimized (190–250°C; ratio of constituents, 0.5: 3) by spectroscopically following the different groups and monitoring the increase of the T_g. Poly(N‐cyclohexyl glutarimide) (65%) containing amide groups (25%) and acid groups (10%) presents a T_g value of 195°C. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 76: 1876–1888, 2000     

C–S bond cleavage in pyridylmethylthioether systems promoted by oxorhenium(V) ion

C–S bond cleavage in pyridylmethylthioether systems promoted by oxorhenium(V) ion has been established performing the reaction of 1,2-bis(2-pyridylmethylthio)ethane(BPT¹), 1,3-bis(2-pyridyl-methylthio)propane(BPT²) and 3,4-bis(2-pyridylmethylthio)-5-methyltoluene (BPT³) with Bu₄N[ReOCl₄] in dry alcoholoic medium. In case of BPT¹ and BPT², new 2-(2-pyridylmethylthio)ethane-1-thiol (L¹H) and 3-(2-pyridylmethylthio)propane-1-thiol (L²H) ligand, respectively were formed in situ through cleavage of one C–S(thioether) bond, resulting in the neutral oxorhenium(V) complexes of formulation [ReO(L¹)Cl₂] (1a) and [ReO(L²)Cl₂] (1b); where as in case of BPT³, binary oxorhenium(V) complex of 3,4-dimercapto-toluene ligand (L³H₂), formulated as Bu₄N[ReO(L³)₂] (1c) through cleavage of two C–S(thioether) bonds. The presence of picolinic acid, as by-product in the filtrates of the C–S bond cleavage reactions in dry alcohol, was detected by treatment of copper(II) salts and GC–MS techniques. But in hydrated alcoholic medium no C–S bond cleavage induced by ReO(V) ion occurred in any of the BPT systems rather the conversion of ReO(V) into perrhenate salt was observed; this reaction mixture, in turn on reaction with copper(II) nitrate trihydrate salt, produce [Cu(BPT)Cl]ReO₄ (2) type complexes. The solid-state structures of complexes 1a and 2a were established by X-ray crystallography.     

Hydrothermal conversion of carbohydrate biomass to lactic acid

We investigated the hydrothermal conversion of the carbohydrates including glucose, cellulose, and starch to lactic acid using NaOH and Ca(OH)₂ as alkaline catalysts. Both catalysts significantly promoted the lactic acid formation. The highest yield of lactic acid from glucose was 27% with 2.5 M NaOH and 20% with 0.32 M Ca(OH)₂ at 300°C for 60 s. The lactic acid yields from cellulose and starch were comparable with the yield from glucose with 0.32 M Ca(OH)₂ at 300°C, but the reaction time in the case of cellulose was 90 s. The mechanism of lactic acid formation from glucose was discussed by identifying the intermediate products. Lactic acid may be formed via the formation of aldoses of two to four carbons including aldose of three carbons, which are all formed by reverse aldol condensation and double bond rule of hexose. This implies that carbon–carbon cleavage occurs at not only C₃? C₄ but also at C₂? C₃. © 2010 American Institute of Chemical Engineers AIChE J, 2010     

A Catalytic Enantioselective Imino‐Reformatsky Reaction

The admission of air in the reaction mixture of imine, ethyl iodoacetate and dimethylzinc, in the presence of 20–30 mol % of inexpensive and commercially available N‐methylephedrine as the chiral ligand, promoted the Reformatsky reaction, without the need for other metals or catalysts. Excellent yields (up to 92 %) and enantioselectivities (83–94 %) were obtained for the tested substrates. The reaction shows a broad scope, and all the imines are prepared in situ, using Me₂Zn as the dehydrating agent.     

Dehydrochlorination behavior of flexible PVC pellets in NaOH solutions at elevated temperature

Flexible PVC pellets were treated at 150–250°C in 0–7M NaOH solutions for 0–12 h. The degree of dehydrochlorination of flexible PVC pellets increased with increasing reaction temperature and was about 100% at 250°C over 5 h. A porous char, 2–16 μm in pore size, was produced. The dehydrochlorination of PVC in the flexible PVC was proceeded by a first-order reaction in alkaline solution. The maximum rate of the dehydrochlorination for flexible PVC was reached at 5M NaOH. The apparent activation energies were 22–35 kcal/mol in 1–7M NaOH for flexible PVC. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 67:2171–2177, 1998     

Kinetics and thermal analysis of copolymerization of m-isopropenyl–α,α′-dimethylbenzyl isocyanate with styrene

The copolymerizations of m-isopropenyl–α,α′-dimethylbenzyl isocyanate (m-TMI) with styrene (STY) was investigated. The weight conversion of the copolymerization reaction increased as the duration of copolymerization increased. The reaction temperature was maintained between 60 and 75°C. Molecular weights of the copolymers decreased with increasing molar fraction of m-TMI in the feed. This study obtained reactivity ratios, Alfrey–Price parameters, Mark–Houwink constant, characteristic ratio, thermal degradation activation energy, difference of reactive propagation activation energy, and intrinsic viscosity for the copolymers. The copolymers were characterized by using elemental analysis (EA), gel permeation chromatography, thermogravimetric analysis, and differential scanning calorimetry. The copolymer chains in solution were observed to have a high degree of stiffness and a lack of rotational freedom. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 73: 2763–2770, 1999     

The Removal of Copper with Dialkyldithiocarbamate Ligands in Condensed Carbon Dioxide

The global kinetics of the oxidation and removal of copper(0) foil were examined in liquid and supercritical CO₂ using tert‐butyl peracetate (t‐BuPA) as the oxidant and dialkyldithiocarbamate lithium salts (Li⁺R₂DTC^–, with R = ethyl, propyl, or n‐butyl) as the chelating agent. The pressure was kept constant (at 240 bar) for all reactions as density was not found to affect the kinetics at pressures above 150 bar. Temperature was varied between 25 and 60 °C and the concentrations of the oxidant and chelating agents were varied to determine the observed overall reaction orders for each species. Interestingly, under our reaction conditions, the observed global reaction was independent of oxidant concentration but varied due to the R₂DTC^– concentration. The Et₂DTC^– had an observed half order reaction dependence, indicating a complex reaction mechanism while the other two R₂DTC^– had first order dependence suggesting diffusion limitations. Arrhenius expressions were determined by the temperature dependent kinetics of the product, Cu(R₂DTC)₂, formation. The apparent activation energy, E_a, for the Et₂DTC^– was 66 kJ/mol, confirming a complex reaction mechanism due to its large value. The apparent activation energies for the Pr₂DTC^– and Bu₂DTC^– were 14 and 17 kJ/mol, respectively. These low energies are consistent with diffusion limitation.     

New Bismaleimide-Silica Hybrid Materials: A Critical Assessment of Properties in Correlation with the Method of Synthesis

New hybrid materials have been prepared by sol–gel technique. They have been obtained from bismaleimide monomers either in reaction with N-(3-triethoxysilylpropyl)furan-2-carboxamide monomer, by a Diels–Alder reaction, or in reaction with (3-aminopropyl)triethoxysilane following a Michael addition reaction. The sol–gel process was conducted with or without adding different amounts of tetraethyl orthosilicate. The structures of the obtained compounds have been confirmed by proton nuclear magnetic resonance and Fourier transform infrared spectroscopy. A comparative study between Diels–Alder- and Michael addition-type products regarding their thermal and mechanical properties was also conducted for samples as obtained from synthesis. The thermoreversible character of the Diels–Alder hybrid materials has been demonstrated with the aids of differential scanning calorimetry and attenuated total reflectance Fourier transform infrared spectroscopy, the results from both methods being in good agreement with each other, and with literature data. The morphology of hybrid materials was studied by the atomic force microscopy, optical microscopy for three different stages: initial (24°C), at heating (150°C), and after cooling at 24°C, and scanning electron microscopy. All data confirmed the driving force for the dispersion of the Si-containing aggregates in the Michael addition series is the dynamic evolution of the sol–gel process, whereas the Diels–Alder series behavior is ruled by the thermoreversible character of the Diels–Alder cycloaddition.     

Effect of Counter Cation on Alkaline Reaction of β-O-4-Type Substructure in Lignin

This study aimed to clarify the effects of counter cations on the alkaline-induced β-O-4 bond cleavage and further reactions of β-O-4-type substructures in lignin. For this purpose, a non-phenolic β-O-4-type lignin model compound, the erythro isomer of 2-(2-methoxyphenoxy)-1-(3,4-dimethoxyphenyl)propane-1,3-diol (veratrylglycerol-β-guaiacyl ether), was treated in a 100% water solution or an aqueous methanol, ethanol, or 1,4-dioxane solution containing LiOH, NaOH, or CsOH as an alkaline source at 150?°C. The rates of β-O-4 bond cleavage were in the order of CsOH?>?NaOH?>?LiOH in all solvents. This order can rationally be attributed to the strength of the interactions between HO^– and the counter cations. Because Cs⁺ has the lowest positive charge density among the counter cations and hence interacts with HO^– most weakly, HO^– can exert its reactivity most actively in the reactions using CsOH. We also discuss how the counter cations affect the profile of reaction products.