Die großtechnische Oxosynthese mit immobilisiertem Katalysator

Industrial Oxo Synthesis with Immobilised Catalyst. The use of water-soluble catalysts represents a significant advance in homogeneous catalysis; “immobilisation” of the catalyst in a second immiscible liquid phase has the effect of “heterogenisation” and allows the advantages of heterogeneous processing (long lifetimes, straightforward technology) to the combined with those of the homogeneous mode (gentle reaction conditions, high activity and selectivity). In particular, the decisive advantage of homogeneous catalysts, viz. the wide range of variation of their steric and electronic properties which can be adapted to the specific reaction at hand, can be exploited for tailoring highly effective catalysts. Moreover, the mode of action of these homogeneous catalysts remains understandable as a model and under the reaction conditions chosen – in complete contrast to the case of many heterogeneous catalytic systems. The first successful industrial application of water-soluble catalysts was in the oxo process of Ruhrchemie/Rhǒne Poulenc. The following article reports on ten years' experience with this process and the HRh(CO)[P(msulphophenyl-Na)₃]₃ catalyst.     

Facile fabrication of 3D interconnected porous boron doped polymeric g-C3N4 with enhanced visible light photocatalytic hydrogen evolution and dye contaminant elimination

Researchers have attempted to developing high-efficiency catalysts for photocatalytic hydrogen evolution and organic pollution elimination simultaneously to alleviate the issues of energy shortage and water pollution. In this work, we fabricated 3D interconnected porous boron doped polymeric g-C₃N₄ catalysts with efficient photocatalytic activity for hydrogen evolution and dye contaminant elimination under visible-light irradiation. The as-fabricated catalysts exhibited significantly enhanced hydrogen evolution (4.37 mmol g ^?1 h^?1) and RhB contaminant elimination (96.37%) activity. Based on characterization and photocatalytic tests, an enhanced mechanism of the superior photocatalytic performance was proposed: 3D interconnected porous structure and B-doping have a synergistic effect on the greatly improved photocatalytic activity. The 3D interconnected structures endowed g-C₃N₄ with a higher specific surface area and abundant active sites and improved the capacity of rapid absorption to facilitate the photocatalytic process. B doping provided enhanced visible-light absorption capacity and a narrowed bandgap and served as a “highway” for electron-hole pairs to facilitate migration and separation and suppress the combination of photogenerated carriers. Besides, the possible mechanism of enhanced photocatalytic performance was elucidated according to the results of characterization measurements and active species analysis.     

Coking characteristics of reforming catalysts

Coking rates were measured for two different γ-aluminas, each with and without platinum, under near commercial conditions using a gravimetric reactor. Coke on catalyst was characterized by a Temperature-Programmed Oxidation (TPO) technique. With a naphtha feed, coke formed on both aluminas at rates related to the respective population of α-sites as measured by IR. For the corresponding Pt on alumina catalysts, coke, as measured by TPO, predominantly formed on sites associated with alumina (“alumina coke”), while coke associated with Pt (“Pt coke”), was relatively minor. With a n-heptane feed, under the same conditions, coke formation on both aluminas was much less than with the naphtha feed. However, the corresponding Pt on alumina catalysts generated comparatively more coke with a higher proportion associated with Pt. A correspondence between this proportion of “Pt coke” and the decline in reforming activity was observed. It is postulated that most of the coke produced during naphtha reforming with an active catalyst is formed by a reaction between α-sites on alumina and certain components in the feed via a polymerization mechanism. This type of coke has minimal effect on the reforming reactivity of the catalyst. However, in n-heptane reforming, about 50% of the coke also results from precursors formed from reactions with Pt. In either case, coke associated with Pt appears to be the probable cause of deactivation.     

Experimental and Modelling Study of a Dual-Layer NH3 Slip Monolith Catalyst for Automotive SCR Aftertreatment Systems

The approach to the development of a chemically and physically consistent mathematical model of ASC dual-layer (SCR + PGM) washcoated monolith converters is herein presented. Steady-state and transient kinetic runs were performed over each one of the two ASC components (SCR and PGM) in the form of powders and also over the two mixed powdered catalysts, thus acquiring information on the interactions between the SCR and the PGM catalytic chemistries. Global kinetic models were fitted to the SCR and to the PGM catalyst data, and validated against experiments performed over both washcoated single-layered SCR and PGM monoliths and over a full dual-layer ASC honeycomb catalyst (SCR layer on top). It was found that the dual-layer (SCR + PGM) ASC architecture grants increased N₂ selectivities compared to a PGM-only washcoat.     

ROLL COATING IN THE PRESENCE OF A FIXED CONSTRAINING BOUNDARY

When a cylindrical roll rotates about its axis while partially submerged in a liquid, as suggested in Figure 1, a layer of the liquid is entrained and withdrawn from the bath. In the absence of a constraining boundary the coating thickness H is found to exhibit a strong dependence on roll speed, as well as on the fluid viscosity and interfacial tension. In a previous publication (Middleman, 1978) from this laboratory we have presented experimental results and a successful data correlation for the case of a roll operating under such conditions that the boundaries of the fluid reservoir exert no influence on the coating dynamics. In this paper the effect of an adjacent constraining boundary is considered, a mathematical model based on lubrication theory is presented, and the data are found to exhibit the general features predicted by the model. Under some conditions it is observed that a uniform coating is not achieved. Instead, a regular set of lines or “ribs” is developed, in the direction of motion. Figure 2 shows this situation. This instability is anticipated and described in the work of others, and a theory of Savage (1977) is evaluated with respect to our own data on critical conditions for onset of “rib” formation. The general features predicted by that theory are consistent with our observations.     

Recycle optimization in non-linear productive chromatography—I Mixing recycle with fresh feed

This paper examines the chromatographic separation of two solutes interacting non-linearly with the sorbent, when only partial separation is achieved at the column outlet, and an intermediate cut of the effluent is recycled. It is shown that, for given feed composition and column size, there is an optimum of the amount of fresh feed injected per cycle; alternately, for given feed composition and amount treated per cycle, there is an optimal column length. This optimum is such that interferences of concentration fronts are minimized in the column. The process is analysed using the “equilibrium theory”, which neglects hydrodynamic dispersion and mass-transfer resistances. Complete analytical solutions are given in the optimal situation, for the case of mass-action law equilibria with unity exponents (Langmuir type equilibrium).The theoretical predictions are compared to experimental results for the separation of Na⁺ from K⁺ by H⁺ eluent in chloride solutions, on a commercial cation-exchanger. The results are also compared to “classical” chromatography (without recycle), and to “two-way” chromatography, presented in a previous paper[1]. With respect to “classical chromatography”, for a given product purity, the optimal recycle process is shown to improve product richness (i.e. concentration of product with respect to solvent) and all performance criteria (eluent consumption, sorbent immobilization, productivity). With respect to “two-way” chromatography, it improves sorbent immobilization and productivity, but yields a poorer Na⁺ product, thus uses more eluent.     

Ethanol dehydration on silica-aluminas: Active sites and ethylene/diethyl ether selectivities

Commercial silica-alumina catalysts prepared by different procedures have been characterized. Both present strong Lewis acidity together with Brønsted sites able to protonate pyridine. No evidence of “zeolitic” bridging OH's but significant heterogeneity of terminal silanol groups, part of which are likely “pseudobridging”, was found. Similar high activity in ethanol conversion but markedly different selectivities to ethylene and diethyl ether were found. They are less active than both zeolites and γ-Al₂O₃. Lewis sites with alumina-like acidobasic neighbor are more selective for ethylene production while Lewis sites with silica-like covalent neighbor are more selective for diethyl ether.     

The thermal decomposition of pure and doped cadmium carbonate: II. Surface and pore structure studies

Specific surface areas and pore structure studies were carried out on pure and doped cadmium carbonate heated at different temperatures. Doping with a different valency cation than the host ion was found to influence appreciably both the extent and location of the surface. Results could be interpreted in terms of anion vacancy mechanism, in which these vacancies could be created in the case of Li⁺ doping and could be annealed in the case of Al³⁺ doping, thus affecting “material” transport which in turn is reflected in changes in the extent and location of the surface. In this respect Al³⁺ ions might act as “inhibitors” for material transport and thus lead to a “stabilised” pore structure. The results implicitly suggest that “material” transport is more significant in affecting the pore structure than changes in the rates of isothermal decomposition.     

Assembled Catalysts—Just Interesting, or Maybe Important?

A lecture held in Honor of Professor Sir John Meurig Thomas on the occasion of his 70th birthday RSC symposium “Perspectives and prospects in catalytic science” at the Royal Institution, London, 3–5 September, 2002. It is beyond doubt that catalysts have had a major influence on the technological development of the world over the last 150 years or so. In this very building, where today we honor Professor Sir John Meurig Thomas, some spectacular advances were made not only in the distant past, by the likes of Faraday and Davy, but also in the more recent past (and dare I say present) by Professor Thomas himself. The in situ studies of catalysts in action, allowing the creation of a basis for rational design, being one of the many shining examples [1]. When working here myself, one of the “Leitmotifs” of Sir John was to ask (his often all-too-exuberant junior colleagues): “It may be interesting, but is it important?” To answer, “It is important, because I find it interesting”, did not cut much ice, so in this spirit, I will be aiming to convince you that assembled catalysts are not just interesting, but also important.     

Surface Science and Catalysis—Studies on the Mechanism of Ammonia Synthesis: The P. H. Emmett Award Address

Abstract

About 5 years ago a Battelle Colloquium on “The Physical Basis of Heterogeneous Catalysis” was held in honor of Professor Emmett where he presented an introductory talk on ″Fifty Years of Progress in the Study of the Catalytic Synthesis of Ammonia″ [1], a field to which he had made significant contributions during this whole period. So why another report on this topic? Justification can perhaps partly be obtained by some of Professor Emmett's concluding remarks which were not completely decisive with respect to the mechanism of this reaction: 'The experimental work of the past 50 years leads to the conclusion that the rate-determining step in ammonia synthesis over iron catalysts is the chemisorption of nitrogen. The question as to whether the nitrogen species involved on the surface is molecular or atomic is still not conclusively resolved. In fact, our own work in this field was mainly induced by this paper, and continuing discussions and correspondence with Professor Emmett were extremely helpful during its progress. I am therefore very much honored to be this year's recipient of the Emmett Award.     

Protected Designation of Origin Extra Virgin Olive Oils Assessment by Nuclear Magnetic Resonance and Multivariate Statistical Analysis: “Terra di Bari”, an Apulian (Southeast Italy) Case Study

We report a study on the chemical characterization of 102 monovarietal micro‐extracted and genetically characterized extra virgin olive oils (EVOOs) from Coratina, Ogliarola Barese and Cima di Mola cultivar, according to “Terra di Bari” (Apulia, southeast Italy) PDO requirement. Three additional geographical mentions, all belonging to the same Bari district (Bitonto, Castel del Monte and Murgia dei Trulli e delle Grotte), were studied and potential microclimate differences were evaluated. Our results indicate the possibility of distinguishing EVOOs from the same “Terra di Bari” PDO with respect to different cultivars and (to some extent) different subareas. In particular, two cultivars (Ogliarola Barese and Coratina), obtained from the same Bitonto area, and a single cultivar (Coratina), obtained from Bitonto and Castel del Monte subareas, were compared to investigate the micro‐area pedoclimatic effect. Finally, ¹H NMR data were found significant for classification purposes of unknown EVOO samples, the results of which were included in the model space, as they were correctly predicted by the OPLS‐DA obtained by ¹H NMR data. This work aims to classify commercial “Terra di Bari” PDO EVOOs by comparison of the declared cultivar and geographical origin with a reference dataset of genetically characterized micro‐extracted monovarietal oils. In conclusion, the effect of the pedoclimatic micro‐areas of origin on the Coratina cultivar, which is the main component of the “Terra di Bari” PDO, has been studied in order to improve the traceability of the raw material used to produce this valuable food.     

Video Microscopy for the Investigation of Gas Phase Copolymerization

Summary: Video microscopy as a tool for investigating olefin gas phase copolymerization is presented for the first time in this paper. The central theme of this work is the study of the comonomer effect shown by an unbridged metallocene catalyst supported on silica. By using video microscopy, it is possible to observe the increase in catalytic activity in terms of particle growth as well as monomer consumption. The observation that a more pronounced induction period in the particle growth profile is shown with increasing propylene concentration led us to investigate the copolymers obtained at different polymerization times using ¹³C NMR analysis and single particle energy dispersive X‐ray (EDX mapping). This allowed us to adapt the “polymer growth and particle expansion model” to the copolymerization. Besides physical causes for the comonomer effect, we wanted to determine whether the catalyst structure plays an important role in the comonomer effect. To this end we investigated two metallocenes bearing the same long bridging unit but differing in the ligand bound to the zirconium center. One metallocene bears a cyclopentadienyl ring, while the other bears an indenyl group. From a close analysis of the ¹³C NMR, it is clear that both catalysts insert ethylene more easily then propylene, probably due to the long bridging unit that results in a narrower aperture angle of the ligand. In addition to this, the indenyl ligand does not allow the formation of propylene blocks even at high propylene concentration.

Snapshot of the polymer particles taken after 165 min of ethylene‐1‐butene copolymerization with catalyst 1 .     

Comparative study on hydrogen-assisted “one-step” methane conversion over Pd–Co/SiO2 and Pt–Co/NaY catalysts

In our laboratory, methane conversion to higher hydrocarbons in “one-step” process under non-oxidative condition at low temperature was first introduced and investigated over Pd–Co/SiO₂ prepared by sol/gel method [Guczi et al., Catal. Lett. 54 (1998) 33] and over Pt–Co/NaY [Guczi et al., Stud. Surf. Sci. Catal. 119 (1998) 295] bimetallic catalysts. It was found that methane conversion in one-step process is at least 2.5 times higher than that measured in “two-step” process on the same catalysts. In the present work, the two-step and one-step processes are compared. It has been established that in one-step process when methane dissociation occurs in the presence of hydrogen containing helium, not only the production of higher hydrocarbons increases but also the selectivity is shifted towards larger molecules. Palladium–cobalt system proved to be more efficient than the corresponding platinum–cobalt catalysts.     

Polymerization of butadiene and isoprene with the NdCl3 · 3TBP-TIBA catalyst system

The isoprene and butadiene polymerization processes with the NdCl₃ · 3TBP-TIBA catalyst system (TBP: tributylphosphate, TIBA: triisobutylaluminium) are studied in detail using an original and very accurate experimental technique. The influences of the initial monomer concentration, the polymerization temperature and the catalyst and cocatalyst concentrations on the conversion, the average molar masses, the polydispersity and the microstructure of the polymers are discussed and explained considering the allylic complexes formed between the neodymium atom and the last monomer unit in the macromolecular chain. A first-order reaction with respect to the monomer was obtained. The calculated value of the activation energy (25.58 kJ mol^?1) is lower than for classical Ziegler-Natta catalysts, thus demonstrating the higher catalytic activity of the NdCl₃ · 3TBP-TIBA catalyst system used. Two types of active centers are possible, as confirmed by GPC data. One of them, which includes aluminium, is more stable and favors the transformation from “anti” allylic units to “syn” allylic units. Thus, the 1,4-cis unit content of the prepared polymers is mainly determined by the TIBA concentration. The catalyst does not react by transfer reactions as TIBA does. The obtained conversions are always higher for butadiene than for isoprene due to a higher tendency of the former to complexate with the neodymium atom and forming allylic complexes.     

“HETEROGENIZING” HOMOGENEOUS CATALYSTS

For many years, it has been customary to classify catalysts as “homogeneous” or “heterogeneous.” The former commonly operate through the formation of “intermediate compounds,” and the latter, by adsorption of the reactants on the catalyst surface. The line between the two is a fine one, for the distinction between adsorption and compound formation is not at all clear, and seems to be becoming less and less clear as we learn more about adsorption. In recent years, several writers [l-7] have stressed the point that there is a good deal of overlap between homogeneous and heterogeneous catalysis. Experimental evidence supporting this point of view is accumulating, and while we are not prepared to say that there is no distinction, we can say with certainty that many homogeneous catalysts can be converted into heterogeneous ones, retaining the advantages of great activity and selectivity inherent in homogeneity and, at the same time, assuming the ready recovery which is the great advantage of heterogenity. In practice, of course, the matter is not quite that simple, for other factors must be considered. On the whole, however, many advantages have been found in the use of heterogenized homogeneous catalysts.     

Comparative study of “ship-in-a-bottle” and anchored heterogenized Rh complexes

Heterogenized rhodium complexes were prepared by two different methods (“ship-in-a-bottle” and anchoring methods) and the catalysts were used in the hydrogenation of simple and prochiral alkenes. The “ship-in-a-bottle” type heterogenized rhodium complexes were active in the hydrogenation of hex-1-ene, cyclohexene, and 1-methylcyclohexene. At the same time the heterogenized catalyst had all the expected advantages of the heterogeneous system, namely easy handling and recyclability. The anchored catalyst could also catalyze the same hydrogenation reactions and showed all the advantages of the heterogeneous catalysts. However, the latter one was much more active in the above hydrogenation reactions than the “ship-in-a-bottle” type catalysts. Moreover, the anchored catalyst showed higher ee in the enantioselective hydrogenation of trans-2-methylpent-2-enoic acid than its encapsulated counterpart.     

Synthesis of higher alcohols from syngas over K/Co/β-Mo2C catalysts

K/Co/β-Mo₂C catalysts were prepared and tested for higher alcohols (C₂₊OH) synthesis (HAS). The catalysts exhibited high catalytic activity and selectivity to C₂₊OH. The effect of Co/Mo molar ratio in the catalysts upon the catalytic performance of HAS was investigated and the best one was at Co/Mo molar ratio of 1/8–1/6. It could be concluded that the Co promoter exerted strong promotion for carbon chain growth, especially for the stage of C₁OH to C₂OH. The XPS spectra revealed that there was a strong synergistic interaction between Co and Mo, and it depended strongly on the Co/Mo molar ratio. The new phases “Co₃Mo₃C” and “Co₂C” formed over Co promoted K/β-Mo₂C catalysts, which might be responsible for the high activity of higher alcohols and hydrocarbons synthesis, respectively.