Effects of metal-support interactions on the hydrogenation of CO over PdSiO2 and PdLa2O3

A study of CO hydrogenation over $\text{Pd}\text{SiO}{}_2$ and $\text{Pd}\text{La}{}_2\text{O}{}_3$ has been carried out for the purpose of identifying the effects of Pd dispersion, Pd morphology, and support composition on the catalytic activity of supported Pd. The specific activity of each catalyst for methanol and methane synthesis was determined from microreactor studies carried out at a fixed set of reaction conditions. Palladium dispersion was measured by H₂O₂ titration, and the morphology of the Pd crystallites, as expressed by the distribution of Pd(100) and Pd(111) planes, was determined from in situ infrared spectra of adsorbed CO. The crystallite morphology of the $\text{Pd}\text{SiO}{}_2$ catalysts is the same, independent of Pd weight loading: 90% of the surface is comprised of Pd(100) planes and 10% of the surface is comprised of Pd(111) planes. By contrast, the crystallite morphology of the $\text{Pd}\text{La}{}_2\text{O}{}_3$ catalysts changes with Pd loading. Primarily Pd(100) planes are exposed at low-weight loadings while Pd(111) planes are exposed at high-weight loadings. The Pd dispersion has little effect on the methanol turnover frequency over both $\text{Pd}\text{SiO}{}_2$ and $\text{Pd}\text{La}{}_2\text{O}{}_3$, for dispersions between 10 and 20%. On the other hand, the methane turnover frequency is independent of Pd dispersion over $\text{Pd}\text{SiO}{}_2$, but increases with decreasing dispersion over $\text{Pd}\text{La}{}_2\text{O}{}_3$. It is further observed that the Pd morphology influences the specific activity of $\text{Pd}\text{La}{}_2\text{O}{}_3$ for methanol synthesis: Pd(100) is nearly threefold more active than Pd(111). For a fixed morphology, the specific methanol synthesis activity of $\text{Pd}\text{La}{}_2\text{O}{}_3$ is a factor of 7.5 greater than that of $\text{Pd}\text{SiO}{}_2$.     

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.     

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.     

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.     

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.     

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.     

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.     

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.     

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.     

Properties of aluminum-fluoride catalysts prepared by the fluoridation of aluminum oxide with trifluoromethane

High-purity AlF₃ has been prepared by allowing γ-Al₂O₃ to react with gaseous trifluoromethane at 670–770 K under 101 kPa total pressure. The use of gaseous trifluoromethane is a new, general method for preparing metal fluorides from metal oxides. AlF₃ prepared using this procedure retained the physical form of the starting γ-Al₂O₃. A $\text{1}\text{16}$-in. γ-Al₂O₃ extrudate, for example, yielded an AlF₃ extrudate with comparable physical dimensions and crush strengths. X-Ray diffraction, BET surface area, pore volume, and surface acidity measurements were employed to characterize various AlF₃ samples. Significant decreases in surface area and pore volume as well as surface acidity occurred upon increasing the concentration of AlF₃ from 90 to 100%. This behavior presumably results from the fluoridation of residual γ-Al₂O₃. AlF₃ extrudates were utilized as supports for Pt and Pd catalysts. Specific benzene hydrogenation activities of these catalysts are comparable to those of Pt and Pd on γ-Al₂O₃. In a unique application, $\text{Pd}\text{AlF}{}_3$ was used to hydrogenate m-diethylbenzene in superacid ($\text{HF}\text{TaF}{}_5$) solution.     

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.     

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.     

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.     

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.     

Reinvestigation of the system C4A.nH2O  C4A.Co2.nH2O

The system C₄A.nH₂O  C₄A.CO₂.nH₂O has been reinvestigated at 22°, 100 % and 65 % relative humidity. Formation conditions, composition and crystallographic properties of the phases C₄A.nH₂O, C₄A.1/2CO₂.nH₂O, C₄A.CO₂nH₂O and their dehydration products have been studied by X-ray and elektron diffraction, infrared and Raman spectroscopy, dynamic weight-loss curves and differential thermal analysis. Only very limited solid solution occurs in the system. X-ray single crystal studies showed the quaternary compound C₄A.1/2CO₂.12H₂O to be trigonal with space group R3c or R$\text{3}$c, lattice parameters $\text{a}{}_{\mathrm{o}}\text{=5.77}\text{a}\text{?}\text{,}\text{C}{}_{\mathrm{<mtext>o</mtext>}}\text{=49.16}\text{a}\text{?}$. C₄A.CO₂11H₂O is triclinic with $\text{a}{}_{\mathrm{o}}\text{=5,}{}_{\mathrm{o}}\text{=5.74}\text{A}\text{?}\text{,}\text{C}{}_{\mathrm{o}}\text{=7.86}\text{A}\text{?}\text{α=92.61°, β=101.96°, δ=120.09°}$. Indexed powder diffraction data of both compounds are given.     

Mechanisms and kinetics of C4AF hydration with gypsum

The mechanisms and kinetics of early stage C₄AF hydration with gypsum was studied by measuring the heat of hydration with a conduction calorimeter. The heat of the reaction was 173 cal/ g-C₄AF. The reaction equation was estimated to be

$\text{C}{}_4\text{AF}\text{+ 4}\text{CaSO}{}_4\text{·2}\text{H}{}_2\text{O}\text{+ 35}\text{1}\text{3}\text{H}{}_2\text{O}\text{→}\text{4}\text{3}\text{C}{}_3\text{(}\text{A}{}_{0.75}\text{,}\text{F}{}_{0.25}\text{)·3}\text{C}\text{S}\text{H}{}_{31}\text{+}\text{2}\text{3}\text{FH}{}_3$

The equation for rate of hydration was ζ = 0.25t as the thickness (ζ) or hydrated C₄AF increased from 0 to 0.6 μm.     

Selectivity for nitrogen formation in NH3 oxidation in wet and dry systems over mixed molybdenum oxides

To overcome the problem of NH₃ formation and reoxidation to NO in automotive dual catalytic systems, it has been suggested to use mixed base metal oxides for the conversion of NH₃ to N₂. The present work reexamines this suggestion and the effect of the prevailing high $\text{H}{}_2\text{O}\text{NH}{}_3$ ratio in the exhaust stream on its applicability. It has been found that, at high $\text{H}{}_2\text{O}\text{NH}{}_3$ ratio in the treated gas, the range of conditions under which the formation of NN bonds prevails is drastically narrowed. The behavior of copper, cobalt and iron molybdates in this surface reaction was examined and that of the copper molybdate was compared with the activity and selectivity of the pure oxides-CuO and MoO₃.     

Compositions of stable and metastable C3A solid solutions crystallized from simulated clinker melts

The crystallization of C₃A from melts which simulate the composition the liquid phase developed in Portland cement clinkers at ～1350°C has been studied. The liquid phase contained CaO, A?₂O₃, Fe₂O₃, SiO₂ and modifiers, typically 4% Na₂O or 5% MgO. Analyses made using an analytical electron microscope and powder X-ray diffraction disclosed that slowly-cooled or annealed preparations yield C₃A containing the least Fe and Si in solid solution whereas metastable crystallizations yield proto-C₃A solid solutions whose tetrahedral sites, normally occupied by A?, may contain up to ～30% Fe and 12% Si replacing A?. It is suggested that clinker C₃A solid solutions have the formula: $\text{[}\text{Ca,Mg}\text{)}{}_{\mathrm{<mtext>72?(</mtext><mtext>n\; +\; m</mtext><mtext>)</mtext>}}\text{)(}\text{Na}{}_{\mathrm{<mtext>2</mtext><mtext>n\; +\; m</mtext>}}\text{)]}{}_{\mathrm{<mtext>72\; +\; </mtext><mtext>n</mtext>}}\text{[(}\text{A}\text{?,}\text{Fe}\text{)}{}_{\mathrm{<mtext>48\; ?\; (</mtext><mtext>m\; +\; z</mtext><mtext>)</mtext>}}\text{(}\text{Si}{}_{\mathrm{<mtext>m</mtext><mtext>\; +\; </mtext><mtext>3</mtext><mtext>4</mtext><mtext>z</mtext>}}\text{)}{}_{\mathrm{<mtext>48\; ?\; </mtext><mtext>1</mtext><mtext>4</mtext><mtext>z</mtext>}}\text{]0}{}_{144}$.