A. Outi I. Krause

Predominant (6,5) Single-Walled Carbon Nanotube Growth on a Copper-Promoted Iron Catalyst

We have developed a magnesia (MgO)-supported iron-copper (FeCu) catalyst to accomplish the growth of single-walled carbon nanotubes (SWNTs) using carbon monoxide (CO) as the carbon source at ambient pressure. The FeCu catalyst system facilitates the growth of small-diameter SWNTs with a narrow diameter distribution. UV-vis-NIR optical absorption spectra and photoluminescence excitation (PLE) mapping were used to evaluate the relative quantities of the different (n,m) species. We have also demonstrated that the addition of Cu to the Fe catalyst can also cause a remarkable increase in the yield of SWNTs. Finally, a growth mechanism for the FeCu-catalyzed synthesis of SWNTs has been proposed.

Etherification and hydration of isoamylenes with ion exchange resin

The simultaneous etherification and hydration of 2-methyl-2-butene and 2-methyl-1-butene were studied in a continuous stirred tank reactor (CSTR). The heterogeneous liquid-phase formation of tert-amyl ethyl ether (TAEE) and tert-amyl alcohol (TAOH) was catalyzed by a commercial sulfonic acid ion exchange resin. Addition of a small amount of water to the feed, caused a marked drop in the overall olefin (isoamylenes) conversion and in the etherification rate. The measured reaction rates of the etherification and alcohol formation were fitted to kinetic models of Langmuir‐Hinshelwood type. These models are based on single site adsorption of every component and the surface reaction being the rate limiting step. The activation energies for the simultaneous etherification and hydration of isoamylenes were 117.7 and 79.9 kJ mol ˇ1 , respectively. The activation energy obtained for the etherification corresponds well with the value of 108 kJ mol ˇ1 obtained in the experiments without water for the etherification of b-olefin (2-methyl-2-butene) with ethanol. # 1998 Elsevier Science B.V.

Successive reactions of gaseous trimethylaluminium and ammonia on porous alumina

Successive reactions of gaseous trimethylaluminium (TMA) and ammonia on porous alumina were studied with the goal of finding suitable process conditions for preparing aluminium nitride (AlN) by atomic layer deposition (ALD), a technique based on separate saturating gas–solid reactions. The reaction of TMA was studied at 353–623 K on alumina dehydroxylated at 473–1073 K, and the following reaction of ammonia at 423–823 K. Reference samples were prepared by reacting ammonia at 623 and 823 K with alumina dehydroxylated at 833 K. The samples were characterised by elemental analysis of carbon and nitrogen and by IR and 1H NMR. TMA reacted with alumina in a saturating manner at 353–573 K. Reaction took place through ligand exchange with surface OH groups, with release of methane, and through dissociation of TMA on pairs of coordinatively unsaturated Al and O ions. Aluminium-bonded methyl groups remained on the surface. Decomposition of TMA occurred at 600 K and above. Ammonia had reacted with most of the methyl groups by 573 K, but 723 K was required to remove them all. Primary, secondary and tertiary amino groups were formed in the reaction, and ammonia molecules were adsorbed on the surface. The average H/N ratio in the amino groups decreased with increasing reaction temperature. Good temperatures for AlN deposition by ALD seem to be any temperature up to 573 K for the TMA reaction and 723 K or above for the ammonia reaction.

Comparative study of TAME synthesis on ion-exchange resin beads and a fibrous ion-exchange catalyst

Abstract The reaction rates to tert. -amyl methyl ether (TAME) with the ion-exchange resin bead catalysts (A16, A35 and XE586) and a fibrous catalyst (SMOPEX-101) were measured as a function of temperature (323–353 K) with stoichiometric amount of reagents fed to a continuous stirred tank reactor. When the reaction rates were assessed against the weight or acid capacities of the catalysts, the activity order was A35>A16>SMOPEX-101>XE586. When the rates were calculated versus the square of the acid capacity, the activities of the catalysts were similar. This indicated a dual-site mechanism. The rates of TAME formation and the isomerisation of isoamylenes as a function of temperature (333–353 K) and the feed MeOH/isoamylene molar ratio (0.5–2.0), as well as the decomposition of TAME, were then measured in a batch reactor with the ion-exchange fibre (SMOPEX-101) as catalyst. Kinetic modelling results favoured a single-site mechanism for the isomerisation and a dual-site mechanism for the etherification. The activation energy was determined to be 116.7 kJ mol −1 for the isomerisation of 2M1B to 2M2B, 92.7 kJ mol −1 for the etherification of 2M1B to TAME and 93.0 kJ mol −1 for the etherification of 2M2B to TAME.

Enhanced glucose to fructose conversion in acetone with xylose isomerase stabilized by crystallization and cross-linking.

The effects of acetone and ethanol on glucose to fructose conversion catalyzed by soluble and cross‐linked crystalline (CLXIC) xylose isomerase were studied. Relative to pure buffer solvent, the fructose production rate was more than doubled in 50% acetone. The same kind of increase in the isomerization rate was not seen with ethanol. Increase both in acetone and in ethanol concentration in the reaction solvent enhanced the production of fructose. At 50 °C in pure buffer solvent the reaction mixture contained 49% fructose in equilibrium and in 90% acetone the fructose equilibrium content was 64%. Furthermore, CLXIC was relatively stable in the presence of high concentration of acetone: 70–80% of activity was left after incubation for 24 h at 50 °C in buffer solutions (pH 7.2) containing 10–90% acetone. In buffer containing 50% ethanol only 2% of the initial activity of CLXIC was retained after 24 h at 50 °C. Soluble xylose isomerase was considerably less stable than CLXIC in both acetone‐ and ethanol‐containing solutions. These results show that the addition of acetone enhances the production of fructose from glucose by enhancing the reaction rate and shifting the equilibrium toward fructose. However, xylose isomerase must be in the form of cross‐linked crystals for maximal activity and stability.

Diffusion and Chemical Reaction in Isoamylene Etherification within a Cation Exchange Resin

The effects of temperature (323–353 K) and the molar ratio of the reagents methanol/isoamylenes (0.3–3.0) on the formation rates of tert-amyl methyl ether (TAME) were measured with different Amberlyst 16 (A16) particle sizes in a continuous stirred tank reactor. The effect of catalyst swelling was studied with several mixtures of reagents (MeOH and IA) and product (TAME) on Amberlyst 16. The particle size influenced the steady state reaction rates most notably at higher temperatures and with substoichiometric feed of the reagents (methanol/isoamylenes), i.e. when the reaction rate should be fast. The estimated effectiveness factors (0.5–1.0) decreased with increasing particle size and increasing temperature. At nonstoichiometric feed ratios of the reagents the value of the estimated effectiveness factor decreased more when methanol was fed in excess. Recalculations of the earlier results of TAME-synthesis demonstrated that when modifying the rate constants obtained from the batch reactor experiments by dividing them by the effectiveness factors, the R-squared values of the regression analysis against temperature increased (improved fit for Arrhenius-type dependency) and the activation energies increased by about 9 kJ mol −1 .

Interaction between the reaction medium and an ion-exchange resin catalyst in the etherification of isoamylenes

tert-Amyl methyl ether (2-methoxy-2-methylbutane, TAME) is synthesised in a liquid-phase reaction of methanol (MeOH) and isoamylenes (2-methyl-1-butene (2M1B), and 2-methyl-2-butene (2M2B)). The reaction rates of the formation of TAME were measured in a continuous stirred tank reactor (CSTR) at the temperature range between 323 and 353 K. The molar ratio of methanol to isoamylenes and the concentration of the reagents were varied in the feed. As the alcohol–isoamylene mixture behaves non-ideality, the equilibrium constants and the kinetic analysis was performed in terms of activities using the Wilson method for activity coefficient estimation. In the first stage, the kinetic parameters of the published kinetic models were estimated with the experimental data. In order to describe the interaction of the reaction medium and the catalyst better, the solubility parameter was added to the kinetic models. The best fit was obtained with the model that included the solubility parameter and was based on the Eley–Rideal (ER) type mechanism.

Comparison of the Various Kinetic Models of TAME Formation by Simulation and Parameter Estimation

Various kinetic models proposed for the synthesis of TAME (tert-amyl methyl ether, 2-methoxy-2-methylbutane) were tested against experimental batch reactor data. The experiments were carried out with methanol/isoamylenes molar ratios varying from 0.2 to 2.0 at temperatures between 333 and 353 K. The range of validity of the various models was evaluated by simulating the experimental conditions and by comparing the adequacy of the models to predict the experimental changes of composition as a function of the catalyst contact time and composition at reaction equilibrium. Activity-based models were found to predict the experimental results better within a wider range of conditions than the concentration-based models. The activity-based models were additionally compared by estimating the values for the model parameters from the experimental data.

CO2 Reforming of n-Heptane on a Ni/Al2O3 Catalyst

Carbon dioxide is widely considered as a greenhouse gas causing global warming. Thus, carbon dioxide storage and catalytic activation for chemical reactions are of great interest. Carbon sequestration in saline aquifers, coalmines, oil and gas wells, and the ocean could be done during the changeover from fossil energy to renewable energy [1]. A potential reaction of carbon dioxide is CO2 reforming, in which the important raw material for chemical industry, synthesis gas (i.e. hydrogen and carbon monoxide) is formed. The CO2 reforming of methane has been already extensively studied, because also methane is regarded as a greenhouse gas [2]. Other potential feedstocks for the CO2 reforming are light, sulphur-free GTL (FischerTropsch) fractions, which are not suitable for gasoline due to low octane numbers. There are only few published studies on CO2 reforming of higher hydrocarbons thus requiring basic experiments with commercial catalyst to study if the reaction is feasible. In this work the reaction was studied with n-heptane (Equation 1) as the model compound for gasoline.

Hydrogenolysis reactions in a batch reactor effect of mass balance inaccuracies on the kinetic parameters

Abstract Studies were made to determine the effect of the phase equilibrium on the mass balances and, thus, on the estimation of kinetic parameters in a batch reactor. The hydrotreating reactions of two model compounds, phenol and thiophenol, were used as test reactions. Losses in the molar balance of aromatic compounds were relatively large when calculation was based solely on the analysis of the liquid samples. To compensate for the lack of quantitative analysis of the gas phase, the gas composition in equilibrium with the analyzed liquid phase under the reaction conditions was simulated. In this way, the molar balances were improved to the level of accuracy needed for the estimation of kinetic parameters. With thiophenol, the accuracy limit was reached at conversions up to 85%. With phenol, the improvement of the mass balances was confused due to coking reactions which were remarkable already at low conversions. However, the simulation clearly increased the precision of the parameters. The routes to the less volatile reaction products were overweighted when data from the liquid phase analysis only were used in the estimation of kinetic parameters.