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Kinetic studies combined with DFT calculations revealed degradation of catalyst to Rh-carbonyl clusters is responsible for the loss of regioselectivity in hydroformylation.

The production of prebiotics like galacto-oligosaccharides (GOS) on industrial scale is becoming more important due to increased demand. GOS are synthesized in batch reactors from bovine lactose using the cost intensive enzyme β-galactosidase (β-gal). Thus, the development of sustainable and more efficient production strategies, like enzyme immobilization in membrane reactors are a promising option. Activated methacrylatic monoliths were characterized as support for covalent immobilized β-gal to produce GOS. The macroporous monoliths act as immobilized pore-through-flow membrane reactors (PTFR) and reduce the influence of mass-transfer limitations by a dominating convective pore flow. Monolithic designs in the form of disks (0.34 mL) and for scale-up cylindric columns (1, 8 and 80 mL) in three different reactor operation configurations (semi-continuous, continuous and continuous with recirculation) were studied experimentally and compared to the free enzyme system. Kinetic data, immobilization efficiency, space-time-yield and long-term stability were determined for the immobilized enzyme. Furthermore, simulation studies were conducted to identify optimal operation conditions for further scale-up. Thus, the GOS yield could be increased by up to 60% in the immobilized PTFRs in semi-continuous operation compared to the free enzyme system. The enzyme activity and long-time stability was studied for more than nine months of intensive use.

Different metathesis catalysts were evaluated regarding their activity for propene production from ethene and trans-butene feedstocks. Nickel, molybdenum, rhenium and tungsten, along with bimetallic nickel-rhenium systems were applied with commercial supports and self-synthesized MCM-41. For the latter support the Si/Al ratio was adjusted as an additional optimization parameter (Si/Al = 60). Attractive activities were observed using Re and NiRe based catalysts at moderate temperatures of 200–250 °C. In contrast, the tungsten-based catalysts were only active above 450 °C. Three catalysts, namely Re/AlMCM-41(60), NiRe/mix (1:1) and W/SiO2 offered propene selectivity’s exceeding 40% at attractive conversion rates. These catalysts were characterized by BET, powder XRD, NH3-TPD and TPR-TPO-TPR cycles. At specific reaction temperatures, reaction-regeneration cycles were performed, which revealed that for the Re and W catalysts the initial reactant conversions and propene selectivity can be recovered. In contrast, for the NiRe catalyst, a continuous, gradual and irreversible decrease of activity was observed. Even though the tungsten catalyst was operated at the highest temperature, no irreversible decrease in conversion and propene selectivity occurred. Therefore, this catalyst has potential as a promising candidate for the synthesis of propene.

Direct dehydrogenation is one well-established process for the provision of short chain alkenes and suffers from rapid catalyst coking. Kinetic modeling of coke built-up and catalyst deactivation due to coking is essential to optimize the total production process consisting of alternating deactivation and regeneration cycles. In this contribution two different deactivation approaches will by studied and evaluated. The first one, introduced by Janssens, describes deactivation as a loss of active catalyst mass depending on the conversion of the reactant. The second, an advanced microkinetic approach, was suggested by Dumez and Froment and explains the loss of activity by coke formation during the production process. Thus, a time dependent activity function is derived and correlated with the reaction rate. Results of experiments performed in a lab scale tubular reactor on a VOx catalyst provided the basis for extending and parametrizing models for reaction kinetics, coke built-up and deactivation, respectively. Temperature and oxygen concentration have been varied to describe the activity dependence on time and reactor position. Finally, modeling the cyclic operation of deactivation and regeneration was possible and allowed optimizing the individual time intervals to maximize total space time yield. A first proposal of an optimized cyclic process regime is presented.

A heat-integrated packed-bed membrane reactor is studied based on detailed, transient 2D models for coupling oxidative and thermal propane dehydrogenation in one apparatus. The reactor is structured in two telescoped reaction zones to figure out the potential of mass and heat integration between the exothermic oxidative propane dehydrogenation (ODH) in the shell side, including membrane-assisted oxygen dosing and the endothermic, high selective thermal propane dehydrogenation (TDH) in the inner core. The developing complex concentration, temperature and velocity fields are studied, taking into account simultaneous coke growth corresponding with a loss of catalyst activity. Furthermore, the catalyst regeneration was included in the simulation in order to perform an analysis of a periodic operating system of deactivation and regeneration periods. The coupling of the two reaction chambers in a new type of membrane reactor offers potential at oxygen shortage and significantly improves the achievable propene yield in comparison with fixed bed and well-established membrane reactors in the distributor configuration without inner mass and heat integration. The methods developed allow an overall process optimization with respect to maximum spacetime yield as a function of production and regeneration times.

It is well known, that forced periodic operation possesses the potential for process improvements. Nevertheless, only a small number of applications is reported, due to complex realization, limited predictability and high inertia of larger units. Nonlinear frequency response (NFR) analysis has proven to predict efficiently time-averaged performance of reactor effluent streams originating from forced periodic changes of one or several input(s). Focus of this paper was an experimental demonstration of forced periodic operation applied to the hydrolysis of acetic anhydride carried out in an adiabatic CSTR. Theoretical results provided a guideline for experiments exploiting simultaneous sinusoidal modulations of the anhydride inlet concentration and the total volumetric flow-rate. Influences of the forcing parameters (amplitudes and the phase difference) were also studied. Confirming the predictions of NFR analysis a significantly higher time-averaged product yields were experimentally achieved compared to conventional steady-state operation with simultaneous modulation of two inputs using an optimized phase shift. The corrections: [https://cer.ihtm.bg.ac.rs/handle/123456789/5415]

A commercial galacto-oligosaccharide (GOS) syrup with prebiotic properties was purified with simulated moving bed (SMB) chromatography to separate undesired side products induced by synthesis reaction mechanism. A promising polystyrene-divinylbenzene resin stationary phase has been characterized with regard to its selective adsorption behavior. The chosen chromatographic system allows a pseudo binary separation of the multi-component GOS syrup mixture exploiting a multi-column continuous chromatographic process. Suitable SMB operation parameters were estimated by means of the equilibrium (triangle) theory, further optimized by modelling the separation in more detail and finally validated experimentally. Changes of temperature, concentration of the feed as well as in the instrumental configuration (open loop, closed loop and 3 zones) were examined with a classical SMB plant in lab scale size. Highly purified GOS products could be obtained with purities up to >99% in the extract and raffinate fractions. A quantitative description of the transfer from batch chromatography to the continuous separation process via SMB technology is provided, indicated significant potential for a scale-up.

Solvent effects on the reaction equilibrium of the 1-dodecene hydroformylation in a decane/N,N-dimethylformamide solvent system is investigated. The reaction was performed at different decane/N,N-dimethylformamide ratios and at temperatures between 368 K and 388 K. The equilibrium concentrations of all reactants and products were determined experimentally. The enthalpy and Gibbs energy of this reaction at the ideal-gas standard state were determined by quantum-chemical calculations in good agreement with literature data. Moreover, quantum-chemically calculated standard Gibbs energies of reaction at infinite dilution in liquid decane/DMF-solvent mixtures allowed a qualitative prediction of the solvent effect on the equilibrium concentrations. Based on the standard Gibbs energy of reaction at the ideal-gas standard state and on fugacity coefficients calculated using the Perturbed-Chain Statistical Associating Fluid Theory, the equilibrium concentrations of reactants and products for the 1-dodecene hydroformylation performed in decane/N,N-dimethylformamide mixtures of different compositions could be predicted in very good agreement with experimental data. © 2017 American Institute of Chemical Engineers AIChE J, 63: 4576–4585, 2017

The rhodium-BiPhePhos catalyzed hydroformylation of n-decenes, as representative long-chain olefins, was investigated in this study experimentally and theoretically. Besides hydroformylation activity, the used catalyst enables significant double bond isomerization which is an essential side reaction. Because of this property, highly selective tandem isomerization–hydroformylation reactions that convert mixtures of n-decenes with internal double bond position to the desired terminal aldehyde undecanal are possible using the Rh-BiPhePhos catalyst. Experimentally, a reaction network analysis strategy was applied to study the coupled main and side reactions separately. Subsequently, a mechanistic kinetic model based on an extended Wilkinson-mechanism was developed that includes all relevant main and side reactions. Fitting the model to the 23 well planned experiments was possible with low deviations between model and experiment, including the tandem reaction. It was found that the tandem reaction shows completely opposite dependencies regarding temperature and synthesis gas pressure compared to the conventional hydroformylation of 1-decene, which is also covered by the model. Hence, strategies for optimal reaction performance of the (tandem isomerization-) hydroformylation were developed and presented.

In this work, an experimental study of the deactivation and regarding a possible regeneration procedure in the ETP-reaction using Ni/AlMCM-41 (Si/Al = 60) was carried out. ETP experiments at different temperatures and long time on-stream were carried out. Characterization of the catalyst after experiments was performed using powder-XRD, N2-physisorption, NH3-TPD, TPO and TEM. At 250 and 350 °C the catalyst did not suffer significant deactivation after 107 h on-stream. Nevertheless, the yield of propene was low. A severe deactivation of the catalyst was observed at 450 °C where propene was the main reaction product. Regeneration of the catalyst after 30 h on-stream at temperatures lower than 350 °C could be performed using a mixture of 5 vol.% oxygen in N2. The regeneration of the catalyst was not possible after 30 h on-stream at 450 °C. Filamentous carbon and Ni reduction are considered responsible of the deactivation of the catalyst at 450 °C. The analysis of the obtained results suggests that a conjunct polymerization process takes place and is the precursor of the reaction products and the carbon species. However, a detailed study of the mechanism of the ETP-reaction should be done for a better understanding of the deactivation of Ni/AlMCM-41.

Herein we report about an efficient isomerization/hydroformylation tandem reaction to convert a technical mixture of decene isomers selectively into the linear undecanal in a thermomorphic solvent system. By applying a rhodium/BIPHEPHOS catalyst a high turnover frequency of 375 h−1 and high regioselectivity of 92% for the linear product are achieved. Yields up to 70% of the linear aldehyde are obtained. The catalyst can be successfully separated from the product using a thermomorphic solvent system consisting of dimethyl formamide (catalyst phase) and dodecane (product phase). The leaching of the rhodium (0.6% of the initial amount) and phosphorus (1.2% of the initial amount) is very low. The catalyst was successfully recycled five times.

This study intends to provide insights into various aspects related to the reaction kinetics of the VOx catalyzed propane dehydrogenation including main and side reactions and, in particular, catalyst deactivation and regeneration, which can be hardly found in combination in current literature. To kinetically describe the complex reaction network, a reduced model was fitted to lab scale experiments performed in a fixed bed reactor. Additionally, thermogravimetric analysis (TGA) was applied to investigate the coking behavior of the catalyst under defined conditions considering propane and propene as precursors for coke formation. Propene was identified to be the main coke precursor, which agrees with results of experiments using a segmented fixed bed reactor (FBR). A mechanistic multilayer-monolayer coke growth model was developed to mathematically describe the catalyst coking. Samples from long-term deactivation experiments in an FBR were used for regeneration experiments with oxygen to gasify the coke deposits in a TGA. A power law approach was able to describe the regeneration behavior well. Finally, the results of periodic experiments consisting of several deactivation and regeneration cycles verified the long-term stability of the catalyst and confirmed the validity of the derived and parametrized kinetic models for deactivation and regeneration, which will allow model-based process development and optimization.

The effect of minor amounts of impurities on the course of chemical reactions is often overlooked. Analyzing commercial 1-dodecene feeds, hydroperoxides were identified as critical impurities. The influence of varying hydroperoxide concentrations in olefin feeds was systematically investigated, experimentally studying rhodium-catalyzed hydroformylation using a diphosphite ligand. A significant loss of n-aldehyde selectivity and linear-to-branched ratio (l/b) was observed for increasing hydroperoxide concentrations. Feeding of an additional ligand and/or purification of 1-dodecene restored the catalyst performance.

The homogeneously rhodium catalyzed hydroformylation of 1-decene was studied using operando FTIR spectroscopy. The bulky chelating diphosphite ligand BiPhePhos was used for catalyst modification. Special emphasis was given to the transformation of the Rh-precursor Rh(acac)(CO) 2 to the activated HRh(BiPhePhos)(CO) 2 catalyst. Under hydroformylation conditions, this complex was found to be the most abundant catalyst species over a wide range of olefin conversion. Other inactive or non-selective rhodium species were not detectable. Analysis of the turnover frequency revealed a first order dependence of the hydroformylation rate with respect to the concentration of 1-decene. These findings indicate that the coordination of the olefin to the Rh-BiPhePhos catalyst is determining the hydroformylation rate of 1-decene.

This work presents an attempt to include more detailed descriptions of adsorption equilibria into the analysis of the rates of heterogeneously catalyzed reactions. The adsorption behavior of ethylene, propylene, oxygen, carbon monoxide and carbon dioxide was studied on a CrOx/γ-Al2O3 catalyst in a broader concentration and temperature range. Dynamic measurements were performed in a tubular reactor applying the Frontal Analysis method, to estimate adsorption isotherms for single components and mixtures individually. The classical Langmuir model and a bi-adsorption model consisting of a Langmuir and a Henry term were parameterized. The temperature dependence of the isotherm model parameters was described via an Arrhenius approach. Using the Multi-Langmuir model and the Ideal Adsorbed Solution Theory, competitive adsorption isotherms for ethylene and propylene were predicted based on the estimated single component parameters. However, the experimental evaluation of the predicted mixture isotherms offered no effect in the concentration range considered. In a higher concentration range the experimental competitive adsorption isotherms were significantly affected. Thus, the considered competitive adsorption models work well. Consequently, the Multi-Langmuir adsorption model is sufficient to describe the investigated model system. With the reliable mathematical description of the adsorption isotherms a more profound description of the reaction rates is possible by separating kinetic and thermodynamic effects.

Double-bond isomerization is a dominant side reaction in hydroformylation of long-chain linear olefins. This isomerization reaction was studied experimentally and theoretically using n-decenes as linear long-chain olefin representatives. On the experimental side, an isothermal batch isomerization experiment was carried out using Rh-BIPHEPHOS as catalyst until the reaction equilibrium was reached. Complete resolution and quantification of all n-decene isomers was achieved using gas chromatography. The observed equilibrium composition was used to extract Gibbs free energy changes of internal n-decenes relative to 1-decene. These were compared to (a) results based on Benson's group contribution method (BGCM) and (b) results from quantum mechanical (QM) calculations. Density functional theory (DFT: BP86, B3LYP, M06-2X) and second order Moller-Plesset (MP2) calculations showed a mean deviation to experimentally determined Gibbs free energy changes of 3–4 kJ mol−1. Using dispersion correction (D3) in DFT calculations reduced the deviations by 1 kJ mol−1. With a mean deviation of only 0.5 kJ mol−1 for Gibbs free energy changes, BGCM was closer to experimental data. Entropy errors in QM calculations were estimated to be responsible for approx. 80% of Gibbs free energy errors.

In this work the direct conversion of ethene to propene was carried out using bimetallic Ni-Mo and Ni-Re over MCM-41 and aluminized MCM-41. It was intended to improve typical Ni based catalysts by including a metathesis active metal. All catalysts were characterized by powder-XRD, N2-physisorption, H2-TPR and TEM. Ni-Mo catalysts revealed the formation of bulk mixed molybdenum-nickel-aluminosilicates on the MCM-41 materials. The contrary case was revealed for the Ni-Re catalysts where a weak interaction between Ni, Re and MCM-41 was observed. All materials were catalytically tested in the gas phase reaction of directly converting ethene into propene using a fixed bed reactor. These results revealed no improvement of the catalytic activity when using Ni-Mo catalyst compared to well known Ni on MCM-41 catalysts. This suggests that Mo is not offering active metathesis sites. In contrast, Ni-Re based catalysts revealed a high selectivity of propene at lower temperatures than the Ni-catalysts. However, the conversion of ethene decreased significantly. Nevertheless, the reduced temperature might avoid the trend of catalyst deactivation observed at high temperature. Still, a deeper characterization of the Ni-Re catalyst is required to understand the role of Re in the direct conversion of ethene to propene.

Continuous chemical reactors are mostly operated under steady-state conditions. However, theoretical studies reveal that forced periodic operation (FPO) can lead to better performance. To predict and optimize FPO, the nonlinear frequency response (NFR) method provides an analytical approach. The presented work is focused on providing theoretical and experimental results devoted to demonstrating both the potential of forced periodic operation and the strength of the NFR method to identify suitable operating conditions. The hydrolysis of acetic anhydride is studied experimentally as a model reaction applying an adiabatic continuous stirred tank reactor (CSTR). Special Issue: 10. ProcessNet‐Jahrestagung und 34. DECHEMA‐Jahrestagung der Biotechnologen 2020: Processes for Future Related to: [https://cer.ihtm.bg.ac.rs/handle/123456789/4042]

The exploitation of methane to produce aromates is already seen for a long time as very attractive. Although investigated intensively, methane dehydro-aromatization (MDA) is far from being applied industrially. MDA under non-oxidative conditions is severely limited by thermodynamics and rapid catalyst deactivation. Mo/MCM-22 was reported as a promising catalyst. Thus, kinetic experiments were performed to parametrize rate expressions and to identify trends regarding the selectivity-conversion behavior including catalyst deactivation. Finally, mass transfer was described mathematically to evaluate the potential of hydrogen-selective membranes within a membrane reactor of the extractor type. Such a removal would be beneficial to overcome the thermodynamic limitations.

A kinetic study of the isomerization of 1-decene using a Rh-Biphephos catalyst was performed in order to parameterize a mechanistic kinetic model to observed experimental data. For the derivation of the kinetic model, a previously proposed catalytic cycle was revised regarding the catalyst pre-equilibrium including the formation of inactive or non-selective Rh-species. In order to estimate the model parameters and to support model reduction, a method based on parameter subset selection was extended and applied. Using this approach, sensitive kinetic parameters were identified and determined for the reduced kinetic model.

Previously developed kinetic and dynamic models of the hydroformylation of 1-dodecene in a thermomorphic multicomponent solvent system (TMS), consisting of DMF, n-decane, and hydroformylation produ...

The experimental and model-based investigation of the palladium-catalyzed methoxycarbonylation of 1-decene using methanol and carbon monoxide is presented. The reaction was studied in a thermomorphic solvent system using the industrially applied ligand DTBPMB in order to describe the kinetics of the main and the most relevant side reactions. Based on a reaction analysis, kinetic models including main influencing variables were derived and successfully parametrized. Thus, inhibition effects of the substrate 1-decene as well as carbon monoxide on the isomerization and methoxycarbonylation rate could be identified.

To design and optimize chemical reactors and bio reactors a profound understanding of kinetics and in particular suitable mechanistic rate models is needed. In chemical reaction engineering the methodology from Christiansen considering elementary kinetics assuming rate-determining steps has been successfully applied. It is hardly considered for enzymatic reactions. In this work, kinetics of formation of the prebiotics galacto-oligosaccharides (GOS) from lactose were investigated with β-galactosidase using batch and dynamic experiments. The rates of the main and most relevant side reactions were quantified. Preliminary investigations were performed to determine the influence of pH, temperature, the amount of enzyme and the initial lactose concentration. To acquire mechanistic understanding instructive perturbation experiments were carried out dosing the substrate lactose and/or the products galactose and glucose either initially or dynamically during fermentation. Based on a postulated catalytic cycle, mechanistic kinetic models were developed considering hydrolysis of lactose, formation of GOS and inhibiting effects of the side products glucose and galactose. A sensitivity analysis was performed applying the subset selection method including model reduction based on singular value decomposition combined with rank revealing QR factorization. The parameterized mechanistic models allowed a good description of batch and dynamic experiments in a broad range of operating conditions.

The hydroformylation of 1-dodecene on a rhodium-biphephos catalyst complex exploiting a thermomorphic multicomponent solvent system was studied experimentally in a batch reactor in order to describe the kinetics of the main and the most relevant side reactions. The formation of the active catalyst was studied in preliminary experiments. Based on a postulated catalytic cycle mechanistic kinetic models were developed considering isomerization, hydrogenation and hydroformylation reactions as well as the formation of not catalytically active Rh-species. The complex overall network was decomposed to support parameter estimation. The isomerization of 1-dodecene, the hydrogenations of iso- and 1-dodecene and the hydroformylations of iso-dodecene and 1-dodecene were investigated as a function of temperature, total pressure and partial pressures of carbon monoxide and hydrogen, respectively. These four sub-networks of increasing size and the total network were analyzed sequentially in order to identify kinetic models and to estimate the corresponding parameters applying model reduction techniques based on singular value decomposition combined with rank revealing QR factorization.

A Ni aluminized mesoporous MCM-41 catalyst was prepared and applied for the direct conversion of ethene to propene. Suitable ethene conversion and good selectivity for the desired molecule propene were achieved. The catalyst placed in a packed tubular reactor was stable for more than 2000 h with time on stream. A reaction network analysis was performed evaluating the product spectrum observed covering a large range of operating conditions. Thereby, temperature and feed concentration can be considered as significant influence parameters on the product distribution. Based on the product spectra, a modified reaction network including a catalytic cycle is suggested, which adds cracking of long-chain olefins to the conventionally considered dimerization/oligomerization and isomerization steps. Following previous publications, the catalyst presented strong deactivation behavior. It was observed that the regeneration conditions (oxygen concentration and regeneration time) are crucial parameters concerning long-time stability. Finally, a cycling reactor operation of deactivation-regeneration steps is suggested.

Poroses Glas ist aufgrund seiner chemischen und physikalischen Eigenschaften sowie der Moglichkeit von gezielten Oberflachenmodifikationen vielfaltig einsetzbar. In dieser Arbeit wird die Synthese und Optimierung von porosen Glaskugeln zur Ruckgewinnung und Enantiomerentrennung chiraler Anasthetika beschrieben. Neben der Charakterisierung mittels Stickstoffsorption und Quecksilberintrusion wird das Retentionsverhalten von Desfluran auf nativen Tragern sowie nach Immobilisierung eines chiralen Selektors chromatographisch untersucht. Porous glass can be widely applied due to favorable chemical and physical properties and the possibility to modify the surface. This work describes the synthesis and optimization of porous glass beads for recovering chiral anesthetics and the separation of the enantiomers. Besides a characterization by nitrogen adsorption and mercury intrusion, the retention behavior of desflurane is investigated in chromatographic experiments with the native support and after immobilization of a chiral selector.

Ni/MCM-41 and Ni/AlMCM-41 were synthesized at different Si/Al ratios and tested in the direct conversion of ethene to propene (ETP-reaction). It was intended to evaluate the effect of modifying the catalyst acidity on the ETP-reaction rather than optimizing its performance. All catalysts were characterized by powder XRD, N2-physisorption, 29Si and 27Al MAS NMR, TEM, NH3-TPD, pyridine-DRITFS, H2-TPR, and TPO. Ni/MCM-41 showed low catalytic activity due to its low acidity. Ni/AlMCM-41 catalyst with a Si/Al ratio of 60 had high catalytic activity. Characterization results revealed that the catalyst structure does not have effect on the catalytic activity. Al could be incorporated into the MCM-41 framework up to Si/Al ratio of 16. Two different Ni-composites on the surface of the MCM-41 and AlMCM-41 were observed. Deeper characterization is required to know the Ni state. Important deactivation was observed at 450 °C. The nature of the carbonaceous species and reaction mechanism require deeper characterization.

The hydroformylation of 1-dodecene was studied using Rh(acac)(CO) 2 and a ligand as a catalyst in a thermomorphic multicomponent solvent (TMS) system consisting of N , N -dimethylformamide, decane and the olefin. High n-aldehyde/iso-aldehydes ratios were obtained with the bidentate phosphite ligand biphephos. In systematic preliminary investigations suitable catalyst/ligand-ratios and catalyst concentrations were determined. In order to derive a simplified reaction network, semi-batch experiments were performed measuring responses to perturbations of pressure and feed composition. From the results obtained the main branches of the reaction network could be identified comprising also isomerizations and hydrogenations of n- and iso-dodecenes. For this simplified reaction network a catalytic cycle is suggested providing the basis for the formulation of a more detailed mechanistic kinetic model.

A template ion exchange approach has been employed to prepare Ni/MCM-41 with varying nickel loadings. The synthesized samples were studied by nitrogen physisorption, X-ray diffraction, atomic absorption spectroscopy, transmission electron microscopy, energy-dispersive X-ray spectroscopy, X-ray photoelectron spectroscopy, temperature-programmed reduction and Fourier transform infrared spectroscopy. Extensive compound formation was found to result from the adopted preparation method. The Ni(II) phase was elucidated to be a nickel silicate with layer structure. Corresponding layers were comprised of an octahedral Ni(II) sheet in between two tetrahedral SiO4 sheets. Nickel compound formation was accompanied by simultaneous dissolution of the support material. The nickel phase was most likely deposited onto the external surface of the MCM-41 particles. Temperature-programmed desorption of ammonia was used to investigate the influence of nickel content on acidity. Moderate acidity was found for the undoped support material. Introduction of nickel led to the formation of two additional types of acid sites with weak and moderate acidity characteristics.

Ni-MCM-41 has been prepared by equilibrium adsorption of different nickel precursors. Nickel citrate and nickel nitrate gave the most active catalysts for the direct transformation of ethene into propene above 250 °C at atmospheric pressure. The maximal ethene conversion at 400 °C was 36% while propene selectivity reached 45%. Analysis of product formation spectra at different temperatures, residence times and inlet compositions revealed reaction kinetics consistent with a sequence of ethene dimerization, positional butene isomerization and propene retro-metathesis.