Stabilization effect of Co for Mo phase in CoMoAl2O3 hydrodesulfurization catalysts studied with X-Ray photoelectron spectroscopy

The promotional effects of Co in $\text{CoMo}\text{Al}{}_2\text{O}{}_3$ hydrodesulfurization (HDS) catalysts were studied by means of X-ray photoelectron spectroscopy. The higher MoO₃-content $\text{Mo}\text{Al}{}_2\text{O}{}_3$ catalysts (10 and 20 wt% MoO₃) contain mobile Mo, which migrates from the pores to the outermost surface layers of the catalysts and segregates to form less active crystalline MoS₂ during the HDS reaction, while in the case of $\text{Mo}\text{Al}{}_2\text{O}{}_3$ (5 wt% MoO₃) catalyst: no migration of Mo was observed. It is revealed that the Co in $\text{CoMo}\text{Al}{}_2\text{O}{}_3$ catalyst inhibits the migration and segregation of Mo and that it keeps Mo effective for the HDS reaction, since no surface enrichment of Mo was observed. It is concluded that stabilization of the Mo monomolecular layer is the main role of Co. The active species of Mo is suggested to have the composition of S/Mo(IV) = 1 on the basis of the sulfur contents of the catalysts under the mild HDS reaction conditions.     

Surface interactions in the system RhAl2O3

Under oxidizing conditions Rh is easily dispersed on γ-Al₂O₃ up to a saturation concentration of > 10% of the support area. The average oxidation state of the dispersed phase is Rh³⁺. Excess Rh is present in the three-dimensional Rh₂O₃ particles. The interaction with the support in air is weak at <600 °C and both the dispersed and three-dimensional phases are easily reduced. Multiple chemisorption of CO, NO, and H is noted on the dispersed phase. In the limit two adsorbate molecules reside on the surface Rh in very dilute samples. The multiplicity is a strong function of Rh concentration and invalidates the measurement of accessible metal area in dilute samples. H₂-O₂ titration, with proper precautions, gives more reliable results, due to a constant surface oxide stoichiometry. In heat treatment (>600 °C), Rh-oxide interacts with both γ-Al₂O₃ and γ-Al₂O₃, diffusing into the subsurface region and the bulk. This process can only be partially reversed by reduction in H₂ (>550 °C). Thus, the measured value of surface Rh will depend also on the prereduction procedure. Exposure of $\text{Rh}\text{Al}{}_2\text{O}{}_3$ catalysts to high temperature under oxidizing conditions will cause loss of active area by both particle growth and by diffusion into the bulk of the support. In concentrated samples one can distinguish among the three Rh states: dispersed on surface, particulate, and dissolved in the support.     

In situ laser raman spectroscopy of the sulfiding of Moγ-Al2O3 catalysts

Raman spectra of sulfided $\text{Mo}\text{γ-}\text{Al}{}_2\text{O}{}_3$ catalysts were obtained using in situ techniques for two sulfiding methods. For samples sulfided by 10% $\text{H}{}_2\text{S}\text{H}{}_2$ at 400 °C, MoS₂ structures were observed. A stepwise sulfiding using 10% $\text{H}{}_2\text{S}\text{H}{}_2$, with spectra recorded at 150, 250, and 350 °C, resulted in observation of molybdenum oxysulfide, reduced molybdate, and surface “MoS₂” phases. Reexposure of these samples to air led to radical modification of the oxysulfide structures as well as transformation of some sulfide phases. A model incorporating terminal and bridging MoS bonding and anion vacancies is proposed. This model is based on the conversion of isolated and aggregated molybdate and MoO₃ species to oxysulfide and reduced molybdenum phases. Conversion of reduced molybdenum phases to sulfides is observed to be slow.     

Ensembling and monolayer parameters for the dehydrogenation of cyclohexane over PtAl2O3 catalyst

The ensembling and the monolayer parameters, such as the number of atoms in an active center (n), the absolute efficiency of an active center (r_n), the number of migration regions (Z₀), average area of migration regions (Δ), fractional surface coverage (θ_c), and the average number of atoms in a region (v), were evaluated for the dehydrogenation of cyclohexane over $\text{Pt}\text{Al}{}_2\text{O}{}_3$ catalyst in vapor phase. The reaction was studied using alumina of two types in the temperature range 225–350 °C at two contact times. Monoatomic ensemble is the active center in the system studied. Dependence of probability of formation of atomic ensemble (P_n) on the average number of atoms in a migration region is also given.     

Conversion of bituminous coal in COH2O systems: 2. pH Dependence

Under $\text{CO}\text{H}{}_2\text{O}$ systems at initial pH values s> 12.6, an Illinois No. 6 coal, PSOC-26, was converted to a fully pyridine-soluble product, with benzene and hexane solubilities of 50% and 18%, respectively. The product gases were H₂ and CO₂. However, the expected $\text{H}{}_2\text{CO}{}_2$ ratio of 1.0 based on the water gas shift reaction was not observed, but the deficit in hydrogen was found in the increased hydrogen content of the coal product. 95% coal carbon recovery and good hydrogen balances were obtained, and the coal products were found to be very similar to those from conventional tetralin systems. The results suggest an efficient base-catalysed process, and that $\text{CO}\text{H}{}_2\text{O}$ systems are useful for coal studies.     

Participation of lewis base on vinyl chloride polymerization with Al(C2H5)3CCl4 catalyst system

The polymerization of vinyl chloride has been investigated using an $\text{Al}\text{(}\text{C}{}_2\text{H}{}_5\text{)}{}_3\text{CCl}{}_4$ catalyst system in the presence of various Lewis bases. Effective Lewis bases are γ-butyrolactone, diglyme and diethylenetriamine which are multidentate. The rate of polymerization is dependent not only on the basicity of the Lewis base used but also on a coordination number of one. The latter is the predominant factor. For the effect of polymeric amines, a tentative hypothesis is discussed.     

Adsorption mechanism of Boscan porphyrins on MoO3' Co3O4and CoMoAl2O3

The adsorption of Boscan porphyrins on $\text{Co-Mo}\text{Al}{}_2\text{0}{}_3$ and molybdenum and cobalt oxides was studied with the aim of establishing the mechanism of vanadium elimination during the hydrodemetallization (HDM) of heavy oils. The results show a change in the e.p.r. signal of V0²⁺ and in the u.v.-visible bands of the porphyrins adsorbed on the catalyst. This change is not observed on the support alone. Under the hydrotreating conditions used, only the $\text{Co-Mo}\text{Al}{}_2\text{0}{}_3$ catalysts show a high demetallization activity. As the support alone does not show HDM activity, the cobalt and molybdenum species on the surface, are the demetallization agents.     

Determination of C4A3S in type K cement and clinker using maleic acid-methanol and ammonium chloride-water as extracting agents

This paper describes a simple chemical method for determining $\text{C}{}_4\text{A}{}_3\text{S}$ in Type K cement and clinker. The method combines two separation procedures, a maleic acid-methanol leach and an ammonium chloride-water leach. All silicates and sulfates, except $\text{C}{}_4\text{A}{}_3\text{S}$, are extracted. The remaining SO₃ in the residue which can be quantitatively determined exists only as $\text{C}{}_4\text{A}{}_3\text{S}$.     

Expansive properties of the mixture C4ASH12 − 2CS III. Effects of temperature and restraint

The effects of temperature and restraint upon the hydration and the expansion of $\text{C}{}_4\text{A}\text{S}\text{H}{}_{12}\text{? 2}\text{C}\text{S}$ mixture compacts in different contact solutions have been investigated. Temperatures above 20°C do apparently hinder the formation of an impervious felt-like layer of ettringite around the $\text{C}{}_4\text{A}\text{S}\text{H}{}_{12}$ particles, thus greatly reducing the retarding effect of the lime. An uniaxial restraint of 1 Kg/cm² is enough to reduce sensibly the expansions which remain however high (about 100%). The results can be satisfactorily interpreted by the reaction and expansion mechanism hypothesized in our previous papers.     

Effects of metal-support interactions on the synthesis of methanol over palladium

The synthesis of methanol and other products from CO and H₂ was studied over Pd catalysts prepared by adsorption of Pd(π-C₃H₃)₂ on MgO, ZnO, La₂O₃, γ-Al₂O₃, SiO₂, TiO₂, and ZrO₂ as well as over a SiO₂-supported Pd catalyst prepared from PdCl₂ and Pd black. Both the activity and selectivity of Pd were affected strongly by the nature of the support and the composition of the Pd precursor. The specific activity for methanol synthesis decreased in the order $\text{Pd}\text{La}{}_2\text{O}{}_3$ ? $\text{Pd}\text{SiO}{}_2$ [derived from PdCl₂] > $\text{Pd}\text{ZrO}{}_2$ > $\text{Pd}\text{ZnO}\text{≈}\text{Pd}\text{MgO}$ > PdTiO₂ > $\text{Pd}\text{Al}{}_2\text{O}{}_3\text{≈}\text{Pd}\text{SiO}{}_2$ [derived from Pd(π-C₃H₅)₂] ? Pd black, while the specific activity for hydrocarbon synthesis decreased in the order $\text{Pd}\text{TiO}{}_2\text{?}\text{Pd}\text{ZrO}{}_2$ > $\text{Pd}\text{La}{}_2\text{O}{}_3$ > $\text{Pd}\text{Al}{}_2\text{O}{}_3\text{≈}\text{Pd}\text{SiO}{}_2$ [derived from PdCl₂] ? $\text{Pd}\text{SiO}{}_2$ [derived from Pd(π-C₃3H₅)₂] ≈ Pd black ? $\text{Pd}\text{MgO}\text{?}\text{Pd}\text{ZnO}$. Dimethyl ether production was observed over four of the catalysts and the activity for formation of this product decreased in the order $\text{Pd}\text{Al}{}_2\text{O}{}_3\text{?}\text{Pd}\text{TiO}{}_2\text{?}\text{Pd}\text{MgO}\text{≈}\text{Pd}\text{ZrO}{}_2$. The effects of support composition on the catalytic properties of Pd are discussed in the light of current ideas concerning metal-support interactions and the acid-base properties of the support.     

Conversion of bituminous coal in COH2O systems: 3. Soluble metal catalysis

The oxyanions of the highest oxidation states of several transition metals, including W, Mo, Cr and Mn, were found to catalyse the liquefaction of Illinois No. 6 coal in $\text{CO}\text{H}{}_2\text{O}$ systems at 400°C. Unlike the high pH (s> 12) required in the base-catalysed system, the effective range for these metal-mediated conversions extend down to pH < 5.0. The benzene-soluble product was found to have a higher $\text{H}\text{C}$ ratio than the starting coal, and the metals were reduced to water-insoluble, lower oxidation states during conversion. A chain scheme is suggested as an explanation for the data.     

Ce4+Ce3+ redox equilibrium in Na2O-B2O3 melts by linear sweep voltammetry

New semi-empirical equations were presented to study the redox equilibria of transition metal ions in molten oxides by linear sweep voltammetry. These equations gave the relation between the peak potential and the polarographic half-wave potential, and contained the Randles-Sevcik equation as an extreme case. The measurements of $\text{Ce}{}^{\mathrm{4+}}\text{Ce}{}^{\mathrm{3+}}$ equilibrium in several Na₂O-B₂O₃ melts were used to verify the equations. The agreement between the electrochemically estimated value of the equilibrium and the other estimated from the chemical analysis of the quenched sample was quite satisfactory. The relation between the $\text{Ce}{}^{\mathrm{4+}}\text{Ce}{}^{\mathrm{3+}}$ equilibrium and the composition of the melt was discussed as the functions of the basicity.     

Preparation and properties of poly(Nε,Nε-dicarboxymethyl-l-lysine)

A new ampholytic homopolypeptide, $\text{poly}\text{(N}{}^{\mathrm{\epsilon }}\text{,N}{}^{\mathrm{\epsilon }}\text{-}\text{dicarboxy-methyl-}\text{l}\text{-lysine}\text{)}$, which has one tertiary amino and two carboxyl groups in the side chain has been derived from a hydrochloride salt of poly(L-lysine). The polymer in aqueous solution seems to be in the coil form with locally extended structure (LES) at neutral pH. In both the acidic and alkaline regions, the molar ellipticity of the polymer changes as a result of change in net charge on the side chain. The conformational changes may be from the coil with LES to other coiled forms. 5–7 M NaClO₄ and 80% aqueous methanol induce the α-helix in the polymer at neutral pH. Divalent cations, Cu²⁺ and Ca²⁺, do not induce any remarkably ordered structures such as α-helix or β-structure in the polymer in aqueous solution at any pH. Ultraviolet absorption studies show an absorption peak of the polymer-Cu²⁺ complex near 240 nm. Dependence of the peak intensity on pH at various q values ($\text{q =}\text{[}\text{Cu}{}^{\mathrm{2+}}\text{]}\text{[}\text{residue}\text{]}$) indicates the two steps of the complex formation. At q less than 0.64, the formation is described only with the first step. An average coordination number for Cu²⁺ at the first step was calculated to be about 2 by the method of Mandel and Leyte. The association constant of Cu²⁺ with the residue at the step was determined from the absorption data to be far smaller than that for the Cu²⁺-EDTA complex. The second step of the formation occurs in the case of large q but the absorption data for the second step cannot be obtained exactly due to precipitation.     

Measurements of anisotropic light scattering: application to the determination of the difference Hh−Hv for θ=π2

By improving the performance of a photogoniodiffusometer, a technique for the accurate determination of various light scattering components has been developed. An original adaptation of the method is the measurement of $\text{(H}{}_{\mathrm{h}}\text{?H}{}_{\mathrm{v}}\text{)}{}_{\mathrm{90°}}\text{(H}{}_{\mathrm{v}}\text{)}{}_{\mathrm{90°}}$, the value of which is dependent only on the scattering particles shape. A few examples are presented.     

N.m.r. of random copolymers of benzyl-l-aspartate with o- and p-nitrobenzyl-l-aspartate

The p- and o-substitution of the benzene ring of poly(β-benzyl-l-aspartate) (PBLA) with a nitro group induces a reversal of the helix sense in the PBLA. Therefore, two series of random copolymers of benzyl-l-aspartate with o- and p-nitrobenzyl-^l-aspartate were prepared in order to study the left-handed→right-handed α-helix transition. The conformational behaviour has been studied by nuclear magnetic resonance spectroscopy and the left-handed→right-handed α-helix transition has been observed from the α-CH shift, from CDCl₃ solutions. Moreover, for each copolymer, the α-helix→coil transition was also studied in $\text{CDCl}{}_3\text{trifluoroacetic acid}$ mixtures. In this case, the transition can be observed from the α-CH shift and from the splitting of the β-CH₂ resonance in the α-helical form also.     

PdSiO2: I. In situ X-ray diffraction studies during treatment and hydrogenolysis

Simple techniques for studies of X-ray diffraction from $\text{Pd}\text{SiO}{}_2$ catalysts during catalytic reactions are reported here. The catalytic activity of $\text{Pd}\text{SiO}{}_2$ of low percentage metal exposed for methylcyclopropane hydrogenolysis at 0 °C is less for catalyst cooled from 450 °C in H₂ than for that cooled in He. This effect appears to result from differing amounts of hydride formation. Ease of formation of hydride decreases with decreasing Pd particle size. Exposing the catalysts with D_h = 13.8 and 29.3% to hydrogen at ~25 °C results in nearly complete conversion of particles of Pd to hydride. Purging with helium (even at 0 °C) reconverts the hydride to palladium, but this reconversion exhibits an induction period; hydride formation is more rapid. Passing hydrogen plus methylcyclopropane results in the conversion into hydride of a substantial fraction of catalyst particles originally present as palladium. The palladium hydride particles of catalyst produced by cooling from 450 °C in H₂ remain as PdH_0.7 during the hydrogenolysis reaction. The lattice parameter of palladium particles is indistinguishable from that of bulk palladium, at least for particle diameters ≥45 Å.     

Redispersion of supported platinum catalysts

The redispersion of platinum on γ-Al₂O₃, SiO₂, and TiO₂ is experimentally studied by means of hydrogen chemisorption, X-ray diffraction, transmission electron microscopy, temperature-programmed reduction, and cyclohexene hydrogenation reaction. The increase in dispersion following treatment in oxygen below 600 °C occurs only for $\text{Pt}\text{γ-Al}{}_2\text{O}{}_3$. For $\text{Pt}\text{TiO}{}_2$, only the presence of chlorine during oxidation brings about a significant redispersion. For $\text{Pt}\text{SiO}{}_2$, redispersion does not occur under any condition. Redispersion can occur only in the presence of platinum oxide which could be stabilized by forming a complex with the support. The method for determining whether or not redispersion will occur for any systems and the conditions needed for redispersion are discussed.     

Constructing cellular network TiO2 photoanode for simultaneous regulation of charge transport and light harvesting properties of quantum dots sensitized solar cells

A novel three dimensional (3D) cellular network structured ${\mathrm{TiO}}_2$ film is developed for CdS/CdSe quantum dots sensitized solar cells (QDSSCs). The vertically net-connected hollow ${\mathrm{TiO}}_2$ photoanode is synthesized via a stepwise hydrothermal method. Benefiting from the hierarchical architecture, the specific surface area is dramatically enhanced thus allowing for loading more quantum dots. Besides, the optical characteristic results demonstrate that the light scattering ability is improved which could be ascribed to the easily trapped incident light in the cellular net-connected ${\mathrm{TiO}}_2$. Furthermore, the one dimensional (1D) structure inherited from nanorods arrays provides direct channels for electron transport accompanied with less recombination. The measured power conversion efficiency (PCE) of the QDSSCs based on this cellular ${\mathrm{TiO}}_2$ photoanode is 4.54%, which is 2.2 times higher than that of the QDSSCs based on the original ${\mathrm{TiO}}_2$ nanorods photoanode. The enhanced photovoltaic performance is ascribed to the higher light harvesting efficiency, improved light scattering property and promoted electron transport. The net-connected photoanode with 1D structure could offer the design of tailored architecture targeting various solar cells.     

Effect of SO3 on formation and hydraulic reactivity of belite

SO₃ accelerates the formation of belite between 1100 and 1300°C. Its effeciency rests on the permanent generation of CaO in statu nascendi by the equilibria $\text{CaSO}{}_4\text{?}\text{CaO + SO}{}_3\text{and SO}{}_3\text{?}\text{SO}{}_2\text{+}\text{1}\text{2}\text{O}{}_2$. Via the gaseous phase this CaO is transported to SiO₂ and reacts there to belite. Only 0.5 – 1.5%SO ₃ are dissolved in belite stabilizing its β-modification, but without increasing the hydraulic reactivity markedly.     

Microscopic study on the polymorphism of Ca3SiO5

The polymorphism of Ca₃SiO₅ has been studied microscopically by following changes in optic properties and modes of twinning of the crystal as a function of temperature. Besides the six modifications already established, a hitherto-unidentified monoclinic phase M₃, which can be characterized only by microscopy at present, has been found to exist just below the rhombohedral phase (R). The transitions $\text{T}{}_2\text{?}\text{T}{}_3\text{et}\text{M}{}_1\text{?}\text{M}{}_2$ that give clear thermal effects on the DTA curve show no corresponding change under the microscope.