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: 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.     

Raman spectroscopic investigation of the effect of H2O on the molybdenum surface species in MoO3Al2O3 catalysts

The Raman spectroscopic characterization of a set of $\text{MoO}{}_3\text{Al}{}_2\text{O}{}_3$ catalysts containing 3 to 25 wt% MoO₃ is presented. Controlled atmosphere measurements show that the Raman spectra of these catalysts are influenced drastically by the water content of the samples. Catalysts calcined in O₂ at 500 °C have spectra very different from previously reported spectra. The MoO stretching vibration is at about 1000 cm^?1 in calcined samples, whereas in H₂O-exposed samples the frequency is near 950 cm^?1. The position of the MoO stretching vibration is shown by repeated H₂O exposure, O₂ calcination cycles to be reversible between 950 and 1000 cm^?1. Models for the interaction of H₂O with the surface molybdate species are presented and discussed with respect to the Raman data.     

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.     

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.     

Nucleophilic substitution onto poly(methylmethacrylate): 4. Dilute solution properties of substituted polymethacrylates

The morphological and hydrodynamic properties of a series of homogeneous fractions of substituted poly(methylmethacrylate) (A units) bearing keto-β-functional groups (B units) of the general structureCOCH₂R, with R = SO_xCH₃ (x = 1,2) or SO₂N(CH₃)₂, were investigated by intrinsic viscosity, light scattering and partial specific volume measurements in dimethylformamide (DMF) solution at 25°C. For molar substitution degrees $\text{DS}{}_{\mathrm{m}}\text{< 0.5}$, the copolymers behave as flexible random coils. The Stockmayer-Fixman-Yamakawa analysis of the $\text{[η]-}\text{M}\text{?}{}_{\mathrm{w}}$ data leads to slightly higher unperturbed dimensions K_o and steric factor σ than those for PMMA, and to stronger chain expansion as a result of the weak hydrogen bonding between DMF and COCH₂R units and a positive X_AB interaction parameter. For $\text{DS}{}_{\mathrm{m}}\text{> 0.5}$ however, copolymers bearing COCH₂SO₂N(CH₃)₂ groups behave as worm-like chains, as derived from the Fujii-Yamakawa analysis of the $\text{[η]-}\text{M}\text{?}{}_{\mathrm{w}}\text{-}\text{v}\text{?}$ data: the persistence length increases from 380 to 570 Å within the $\text{DS}$_m range 0.57–0.75. This transition from a random coil to a worm-like chain for $\text{DS}{}_{\mathrm{m}}\text{> 0.5}$ was tentatively correlated with the accumulation of B units in sterically hindered and self-associated short blocks of average length l_B ? 1.6 which provide drastically increased rigidity to the copolymer chain.     

Dielectric constants of coal-derived liquids and slurries with coal at 750 MHz

The real part of the complex dielectric constants of SRC-I recycle solvent, SRC-II naphtha, middle distillate and heavy distillate, and tetralin were measured over the temperature range of 23° to 140°C. Values were strongly temperature dependent, generally increasing with temperature and increasing in the sequence naphtha < heavy distillate < recycle solvent < middle distillate, and were related to the phenolic contents of the liquids. The temperature dependence was attributed to the viscosity which in turn affects the relaxation behaviour of the dipolar molecules in the liquid. Association-dissociation equilibria of the polar components also affect the dielectric constant. Measurements of slurries of the SRC-I recycle solvent with coal show that the real part of the dielectric constant, $\text{}\text{?}$g3′, is given by the Looyenga equation, $\text{}\text{?}\text{g3′ = [ε′}\text{1}\text{3}{}_2\text{+φ}{}_1\text{(ε′}\text{1}\text{3}{}_1\text{?ε′}\text{1}\text{3}{}_2\text{)]}{}^3$, where ε′₁ and ε′₂ are respectively the real parts of the dielectric constant of the coal and the solvent and φ₁ is the volume fraction of the coal.     

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 $\text{M}\text{?}{}_{\mathrm{<mtext>n</mtext>}}\text{> ca. 10 000}$.     

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.     

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.     

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.     

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 $\text{Pd}\text{SiO}{}_2$.     

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 $\text{?W}\text{?I}{}_2$.     

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.     

Interaction parameters in the n-undecane/butanone/poly(dimethyl siloxane) system

Intrinsic viscosities, [η], second virial coefficients, A₂, preferential solvation coefficients, λ, and binary interaction potential as measured by light scattering, g₁₂, for the system n-undecane(1)/butanone(2)/poly(dimethylsiloxane) (3) have been determined at 20.0°C. The system shows cosolvent character, as the inversion in λ and the maxima in A₂ and in [η], at $\text{ø}{}_{10}\text{?0.65}$, seem to indicate. (g₁₃ – sg₂₃) and the ternary interaction potential, g_T, and its derivatives on system composition, and , have been evaluated. Global interaction parameters, χ_m3, have also been evaluated and a critical analysis on the approximations usually followed for χ_m3 calculations is undertaken.     

Conversion of work of deformation to heat in polymers

The time dependence of the conversion of mechanical work of deformation to heat in polymers is investigated using viscoelastic models. The deformation chosen is a constant strain rate, $\text{?}\text{?}{}_0$, in tension for t?t₀ and a constant strain $\text{?}{}_0\text{=}\text{?}\text{?}{}_0\text{t}{}_0$ for t?t₀. For a simple Maxwell model with only one relaxation time, τ, the ratio of heat produced to work done (‘conversion fraction’) is calculated as a function of time for different values of $\text{t}{}_0\text{τ}$. At t=t₀ the conversion fraction is high only when τ?₀. For a continuous Maxwell model with a distribution of relaxation times H(τ) we obtain the result that the conversion fraction is near 100% at t=t₀ if H(τ) is not peaked strongly in the region τ>0·1t₀ but extends with reasonable values into the region τ < 0·1t₀. A formula is given which allows the calculation of the conversion fraction at t=t₀ from the distribution of relaxation times H(τ).     

Studies of cyclic and linear poly(dimethyl siloxanes). 4. Bulk viscosities

The bulk viscosities η of over fifty sharp fractions of cyclic and linear poly(dimethyl siloxanes) in the weight-average molecular weight range $\text{500 <}\text{M}\text{?}{}_2\text{< 25 000}$ have been measured at 298 K using a cone- and-plate microviscometer. In the Iow molecular weight region $\text{M}\text{?}{}_{\mathrm{W}}\text{< 1000}$) the η values for the cyclics were found to be at least three times as large as the values for the corresponding chain molecules. By contrast, in the highest molecular weight region ($\text{M}\text{?}{}_{\mathrm{W}}\text{> 16 000}$), the η values for the cyclics were approximately one-half those for the corresponding linears. Cyclics and linears containing about one hundred skeletal bonds were found to have similar bulk viscosities. The temperature dependence of the bulk viscosities of eighteen of the cyclic and linear fractions were investigated, and the relationship $\text{η = A}\text{exp}\text{(}\text{E}{}_{\mathrm{<mtext>visc</mtext>}}\text{RT}\text{)}$ was used to deduce values for the energies of activation for viscous flow E_visc and the constants A.     

Chemical beneficiation of coal with aqueous hydrogen peroxide/sulphuric acid solutions

The removal of sulphur and ash from coal treated with aqueous hydrogen peroxide/sulphuric acid solutions has been studied at ambient temperature, under a variety of experimental conditions. Almost complete elimination of the sulphate and the pyritic sulphur was observed in most cases, as well as substantial reduction in the ash content. The other components of the organic coal matrix were not affected to a significant extent, indicating high selectivity of the $\text{H}{}_2\text{O}{}_2\text{H}{}_2\text{SO4}$ system towards sulphur oxidation. An optimal H₂SO₄ concentration was established, above which the acid was found to have an adverse effect on the oxidation of pyrite by hydrogen peroxide.     

Solid and liquid state relaxations in spin-labelled poly)ethylene glycol) at high temperatures (T>Tg)

Free and covalently bonded (esterified) nitroxyl radicals experienced in poly(ethylene glycols) (PEG; $\text{M}\text{?}{}_{\mathrm{n}}$ 200–22 000) at temperatures T >T_g several different isotropic rotational relaxation regions. As a first approximation it was assumed, that in the polyglycols $\text{M}\text{?}{}_{\mathrm{n}}\text{? 1000}$ there are at least three rotational relaxation regions: the liquid state (I), the melting state (II) and the solid state (III). The existence of the fourth region, the frozen solid state (IV), was also concluded. The existence of the relaxation region (II) indicated the close interaction between radicals and the crystalline phase. The order of rotational activation energies (E_a) was E^II_a >E^III_a >E^I_a >E^IV_a ($\text{M}\text{?}{}_{\mathrm{n}}\text{? 1000}$). In the polymer melts (I) E_a values of free and bonded radicals first diminished as a consequence of the decrease of the end group effect and they achieved constant high molecular weight values (～15 and 25 kJ respectively). E_a changed in the solid state as a function of $\text{M}\text{?}{}_{\mathrm{n}}$ principally in the same manner except of the higher numerical values (～40 kJ).E_a of free and covalently bonded radicals in the transition region (II) gained a maximum at $\text{M}\text{?}{}_{\mathrm{n}}$ 1550 (125 and 170 kJ) and another at $\text{M}\text{?}{}_{\mathrm{n}}\text{> 9500}$ (130 and 165 kJ) expressing the high degree of order in these polymers in the solid state.The results obtained correlated well with the proton magnetic resonance measurements but they did not correlate with the amorphous dielectric relaxation measurements.It was concluded that the following factors may affect the rotational relaxations of nitroxyl radicals in PEG: the free volume of the polymer, the crystallinity, the chain packing and the end-group effect. The segmental character of the relaxation process was clearly indicated.     

Absorption of sulphur dioxide by sodium humates

As part of a programme for assessing the potential of basic humates as stack gas scrubbing media, the reaction of sodium salts of coal derived humic acids (HA) with sulphur dioxide was investigated. The principal absorption mechanism was found to be acid-base:

$\text{Na-HA(aq) + SO}{}_2\text{(g) + H}{}_2\text{O}\text{?}\text{HA(s) + HSO}{}^{\mathrm{t-}}{}_3\text{(aq) + Na}{}^{\mathrm{+}}\text{(aq)}\text{Soluble sodium}\text{Insoluble humic}\text{humate}\text{acid}$

However, formation of a sulphur dioxide-HA ‘complex’ was observed under conditions (low pH, high temperature) which favoured conversion of a significant fraction (> 5%) of dissolved sulphites to the SO₂(aq) ‘H₂SO₃’ form. Greater complexation of SO₂(aq) was observed for HA preparations which had been stored under basic conditions for periods up to two years. Reversibility of absorption and desorption was demonstrated. Similar experiments with hydrogen sulphide revealed no significant reaction with sodium or iron(III) humates.