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 $\text{Pd}\text{SiO}{}_2$.     

Catalytic activities of binary metal oxides containing iron for hydrocracking of benzyl phenyl ether and diphenyl ether

Hydrocracking of benzyl phenyl ether and diphenyl ether has been carried out over a series of iron catalysts (Fe₂O₃, Fe₂O₃Al₂O₃, Fe₂O₃ZnO, Fe₂O₃ZrO₂, Fe₂O₃MgO and Fe₂O₃SiO₂) and reference catalysts ($\text{CoOMoO}{}_3\text{Al}{}_2\text{O}{}_3$, $\text{NiOMoO}{}_3\text{Al}{}_2\text{O}{}_3$ and SiO _Al₂O₃) to search for active and selective catalysts, and to elucidate the catalyst properties of relevance for CO bond cleavage. Among the iron catalysts, Fe₂O₃ZnO, Fe₂O₃ZrO₂ and Fe₂O₃MgO exhibited relatively high activities and selectivities. The important property of catalysts relevant to hydrocracking of the ethers is the ability to accomplish hydrogenation. Acidic properties of the catalysts cause condensation and rearrangement of the reactants. The features of the iron catalysts are compared with those of molybdenum catalysts, and the reaction mechanisms discussed.     

Assessment of the activities of catalysts for the hydrocracking of coal by means of hydrogen evolution

A close relation has been found between hydrogen evolution from coal-catalyst and pitch-catalyst systems and catalytic activities of liquefaction reactions. A MoO₃?TiO₂ catalyst has the highest activity and the order of activity of the catalysts for hydrogen evolution is: MoO₃?TiO₃> MoO₃?SiO₂>10% $\text{Fe}{}_2\text{O}{}_3\text{TiO}{}_2\text{?AI}{}_2\text{O}{}_3\text{>}\text{coal alone}$. The same trend was observed for benzene-soluble materials for the hydrocracking of Akabira Coal.     

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.     

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.     

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.     

Polymerization of poly(dimethylsiloxane) macromers: 1. Copolymerization with styrene

The synthesis and characterization of methacrylate-ended macromers ($\text{M}\text{?}{}_{\mathrm{<mtext>n</mtext>}}$ 500 to 10 000) and their copolymerization with styrene (M₂) is described. The experimental errors in the values of the reactivity ratios r₁ render them meaningless. Values of r₂ can be determined with more precision and increase from 1.06 to 1.55 as the molecular weight of the macromer increases. This behaviour is due to steric effects, not diffusion-controlled propagation. It is shown that the assumptions that $\text{1 > r}{}_1\text{[}\text{M}{}_1\text{]}\text{[}\text{M}{}_2\text{]}$ and $\text{r}{}_2\text{>}\text{[}\text{M}{}_1\text{]}\text{[}\text{M}{}_2\text{]}$ are only valid for macromers of $\text{M}\text{?}{}_{\mathrm{<mtext>n</mtext>}}\text{> ca. 10 000}$.     

Selective steam reforming of aromatic hydrocarbons: IV. Steam conversion and hydroconversion of selected monoalkyl- and dialkyl-benzenes on Rh catalysts

Steam conversion and hydroconversion of a series of monoalkylbenzenes (C₆H₅R, R = C₂H₅, n-C₃H₇, i-C₃H₇, tert-C₄H₉) and of dialkylbenzenes (o- and p-xylenes) are studied at 713 K and atmospheric pressure on supported rhodium catalysts ($\text{Rh}\text{Al}{}_2\text{O}{}_3$, $\text{Rh}\text{SiO}{}_2$ and $\text{Rh}\text{TiO}{}_2$), and compared to the toluene steam dealkylation previously studied on the same catalysts. Three types of reaction, namely dealkylation (CC rupture on the side chain), dehydrogenation (on the side chain), and degradation (i.e., ring opening) account for virtually the whole product spectrum. Isomerization, transalkylation, and dehydrocyclization reactions may, in general, be discounted. In the presence of steam, the main initial product of monoalkylbenzene dealkylation is invariably benzene, but the splitting of the CC bonds in the middle or end of the side chain always increases with conversion. As a rule, the specific activities (per metal site) in dealkylation decrease with the degree of substitution in the alkyl group (primary > secondary > tertiary > quaternary carbon). On the other hand, the specific activities in ring opening remain constant for all the hydrocarbons and even for the benzene. In the presence of hydrogen, multiple CC bond splittings are invariably observed and benzene is no longer, in general, the principal initial product. The activities in ring opening are equally constant, but at a lower level than in steam conversion. These results are in overall agreement with the model of the dual active sites: sites I appear operative for dealkylation and dehydrogenation, whereas ring opening takes place at sites II with a high probability, independent of the alkyl group size. Possible adsorbed species on each type of site are described. An attempt is made to rationalize the effects of assorted selectivity-determining factors (metal particle size, support effects, selective poisons such as S and CO) in terms of electronic or geometric effects.     

Studies of cyclic and linear poly(dimethyl siloxanes): 10. Calculations of radii of gyration

A Monte Carlo method has been devised for calculating the conformation-dependent properties of cyclic poly(dimethyl siloxanes) (PDMS), using Flory, Crescenzi and Mark's rotational isomeric state model. Calculated values of the mean-square radii of gyration 〈s²_r〉 of ring molecules unperturbed by excluded volume effects and containing 8–100 skeletal atoms are compared with the 〈s²_l〉 values for the corresponding unperturbed chain molecules. Exact enumeration methods were also employed for rings $\text{[(}\text{CH}{}_3\text{)}{}_2\text{SiO}\text{]}{}_{\mathrm{<mtext>w</mtext><mtext>2</mtext>}}$ with w ? 24 and the results found to be in close agreement with those obtained by the Monte Carlo method. The ratio $\text{〈s}{}^2{}_{\mathrm{l}}\text{〉}\text{〈s}{}^2{}_{\mathrm{r}}\text{〉}$ was found to attain limiting values close to 2.0 for w > 30, in agreement with theoretical predictions.     

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: $\text{[}\text{Ca,Mg}\text{)}{}_{\mathrm{<mtext>72?(</mtext><mtext>n\; +\; m</mtext><mtext>)</mtext>}}\text{)(}\text{Na}{}_{\mathrm{<mtext>2</mtext><mtext>n\; +\; m</mtext>}}\text{)]}{}_{\mathrm{<mtext>72\; +\; </mtext><mtext>n</mtext>}}\text{[(}\text{A}\text{?,}\text{Fe}\text{)}{}_{\mathrm{<mtext>48\; ?\; (</mtext><mtext>m\; +\; z</mtext><mtext>)</mtext>}}\text{(}\text{Si}{}_{\mathrm{<mtext>m</mtext><mtext>\; +\; </mtext><mtext>3</mtext><mtext>4</mtext><mtext>z</mtext>}}\text{)}{}_{\mathrm{<mtext>48\; ?\; </mtext><mtext>1</mtext><mtext>4</mtext><mtext>z</mtext>}}\text{]0}{}_{144}$.     

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.     

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.     

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.     

Formation mechanism and ceramic process of the ferroelectric perovskites: Pb (Mg13Nb23)O3 and Pb (Fe12Nb12)O3

The formation of the $\text{Pb}\text{(}\text{Mg}{}_{\mathrm{<mtext>1</mtext><mtext>3</mtext>}}\text{Nb}{}_{\mathrm{<mtext>2</mtext><mtext>3</mtext>}}\text{)}\text{O}{}_3$ and Pb $\text{(}\text{Fe}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}$$\text{Nb}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{)}\text{O}{}_3$ phases with a perovskite type structure is directly dependent on the reactivity of magnesium and ferric oxides to other phases belonging to the binary system PbO  Nb₂O₅. Moreover, it is shown that the ceramic process influences the proportion of perovskite phases in comparison with parasite phases and also the densification of the samples. The optimization of the ceramic process allows to obtain a pure $\text{Pb(Fe}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{Nb}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{O}{}_3$ phase, but as far as $\text{Pb(Mg}{}_{\mathrm{<mtext>1</mtext><mtext>3</mtext>}}\text{Nb}{}_{\mathrm{<mtext>2</mtext><mtext>3</mtext>}}\text{)}\text{O}{}_3$ is concerned, a parasite phase is never entirely eliminated.     

Structural study of hexane-soluble products from hydroliquefaction of three Yallourn brown coal lithotypes over molten salt catalysts

The hexane-soluble fractions of hydroliquefied products from three Yallourn brown coal lithotypes have been separated into five fractions by combined silica-alumina packed column chromatography. Analyses of various fractions by g.c.-m.s. permitted the identification of ≈50 components in the saturate fraction and 40 components in the diaromatic fraction, together with 30 components in the monoaromatics. The components identified were quite similar among hexane-soluble portions of all three lithotypes. A marked predominance of even carbon number alkane (C₂₃-C₂₉) was observed in the hydrocarbon fractions from pale lithotype over $\text{ZnCl}{}_2\text{KCl}$, and medium light lithotype over both pure ZnCl₂ and $\text{ZnCl}{}_2\text{KCl}$. However, medium dark lithotype over both melt catalysts produced a saturate fraction with an odd carbon number(C₂₂-C₂₈) preference. Based on spectral methods, Soxhlet extracts obtained from untreated lithotypes (hexane and benzene solubles) were characterized as complex mixtures of higher molecular weight(300–1000) aliphatic hydrocarbons, which were supposed to be a precursor of the saturates produced from the corresponding lithotype in the catalytic hydroliquefaction.     

Experiments on the small-strain behaviour of crosslinked natural rubber: 1. Torsion

The torsional behaviour of 1, 3 and 5 phr peroxide crosslinked natural rubber has been characterized over a range of strains from near the undistorted state (γ ≈ 0.017) to γ ≈ 1.0. Isochronal measurements of both torque and normal force were used to calculate values of the derivatives of the strain energy function W with respect to the first and second stretch invariants I₁ and I₂. In the course of our work we found that, contrary to many reports in the literature, $\text{?W}\text{?I}{}_1$ was affected significantly by the amount of crosslinking. Finally for the 1 phr peroxide crosslinked rubber it was found that, while ageing for 14 months at ambient conditions did not significantly affect the small-strain torsional modulus, $\text{G = 2(}\text{?W}\text{?I}{}_1\text{+}\text{?W}\text{?I}{}_2\text{)}$, it did significantly affect the individual derivatives $\text{?W}\text{?I}{}_1$ and $\text{?W}\text{?I}{}_2$.     

Studies of a CuY zeolite as a redox catalyst

The stability and behavior of CuY in the redox cycles with $\text{CO}\text{O}{}_2$, $\text{H}{}_2\text{O}{}_2$, and $\text{CO}\text{NO}$ have been studied using a microbalance operating in the flow mode and with a standard (BET) volumetric system. When CO was used as a reducing agent CO₂ was produced, thus removing oxygen from the zeolite lattice, but when H₂ was used only some of the H₂ consumed was evolved as H₂O. The rest was retained as lattice OH groups, but this was minimal when H₂ was used after treating the sample with CO. Oxidation with NO produced only N₂. At 500 °C the sample was stable and could be reversibly oxidized and reduced through many cycles using either $\text{CO}\text{O}{}_2$ or $\text{NO}\text{CO}$. In all cases the ratio $\text{O}\text{Cu}$ was close to 0.5, i.e., $\text{1e}\text{Cu}$. Treatment in CO at higher temperatures did not affect the reversible nature of the oxidation, but now the valence change was substantially larger; it approached $\text{2e}\text{Cu}$. The crystallinity of the exchanged zeolite was studied using X-ray diffraction and by measurement of the pore filling with liquid N₂. No significant changes could be detected after the different treatments, even those performed at 750 °C. Temperature-programmed reduction, temperature-programmed oxidation, and X-ray diffraction studies were made and the different maxima are reported. CuO and Cu ^o appeared in the oxidized and reduced samples, respectively, after treatment at 750 °C in CO but not at lower temperatures. Subsequent redox cycles at 500 °C did not appear to affect the size or amount of Cu ^o crystallites. CuY was active in the oxidation of CO with O₂ or NO. Its activity was lower than that of FeY zeolite when it exhibited an oxygen-carrying capacity of 0.5 $\text{O}\text{Cu}$. Treatment with CO at 750 °C, however, reversed the situation. Kinetic results showed that the fresh CuY catalyst was close to zero order in CO and fractional order in O₂ with an activation energy of 15 kcal/mole. After treatment at 750 °C in CO, the rate law became dependent upon the $\text{CO}\text{O}{}_2$ ratio. It was close to first order in CO and zero order in O₂ under oxidizing conditions ($\text{CO}\text{O}{}_2\text{≤ 2}$), but the orders were reversed under reducing conditions ($\text{CO}\text{O}{}_2\text{> 2}$). The activation energies were 12 and 15 kcal/mole, respectively. The data suggested that the Cu²⁺ with bound oxygen are the species active in the oxidation reaction.     

The kinetics of the catalytic hydrogenolysis of ethane over Ni/SiO2

The rate of hydrogenolysis of ethane over a Ni/SiO₂ catalyst, studied over a large range of pressure and of temperature, is shown to be related to the degree of hydrogen coverage θ_H, by the equation: with K₀ nearly equal to the number of ethane molecules colliding with the Ni surface, E₀ = 14 ? 1 kcal/mole, Y = ?1 ? 2 and X = 15 ? 2. The rate-limiting step is believed to be the irreversible, dissociative adsorption of ethane on an ensemble of at least 12 adjacent Ni atoms, free from adsorbed hydrogen, resulting in the complete cracking of C₂H₆: C₂H₆ + 12Ni → 2

Irreversible adsorption of ethane is assumed to compete with the reversible adsorption of hydrogen. This mechanism, which is compared with those proposed earlier, is in good agreement with data on ethane adsorption studied by magnetic methods, and with a study of ethane hydrogenolysis over NiCu/SiO₂ catalysts.     

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.