Gas phase hydroformylation of ethylene using organometalic Rh-complexes as heterogeneous catalysts

The heterogeneously catalysed gas phase hydroformylation of ethylene to propionaldehyde was studied over solid RhCl(PPh₃)₃ and RhCl(CO)(PPh₃)₂. At 3 bar and 185 °C, an active phase formed from RhCl(PPh₃)₃ which was different from RhCl(CO)(PPh₃)₂ under the reaction conditions studied. The selectivity of RhCl(PPh₃)₃ to propanal was much better than that of supported Rh-metal. Thus, solid metal-complexes operated in gas phase reactions clearly hold promise as a new class of heterogeneous catalysts.     

Influence of potassium on the competition between methane and ethane in steam reforming over Pt supported on yttrium-stabilized zirconia

The effect of addition of potassium to Pt supported on yttrium-stabilized zirconia (PtYSZ) catalyst for steam reforming of methane, ethane and methane/ethane mixtures was explored. Addition of potassium has a positive effect on preferential steam reforming of methane in mixtures of methane and ethane over Pt/YSZ catalysts. The activity of potassium-modified catalysts increased with time-on-stream during steam reforming of mixtures of methane and ethane, while the ratio of reaction rates of methane and ethane remained constant. Most importantly, it was demonstrated that the presence of potassium prevents competition between methane and ethane during steam reforming. The reaction rate ratio in methane/ethane mixtures is changed from preferential ethane reforming on PtYSZ towards preferential methane conversion as a result of addition of potassium.     

XAFS spectroscopy; fundamental principles and data analysis

The physical principles of XAFS spectroscopy are given at a sufficiently basic level to enable scientists working in the field of catalysis to critically evaluate articles dealing with XAFS studies on catalytic materials. The described data-analysis methods provide the basic tools for studying the electronic and structural properties of supported metal, metal–oxide or metal–sulfide catalysts. These methods include (a) fitting in R-space, (b) application of the difference file technique and (c) control of the fit procedure with k ¹ and k ³ weighting with the help of phase- and amplitude-corrected Fourier transforms. This revised version was published online in June 2006 with corrections to the Cover Date.     

CO-induced decomposition of small Pt particles in K-LTL zeolite

Reduced Pt/K-LTL has been studied with XAFS spectroscopy before and after CO admission at room temperature. The results of the EXAFS data-analysis show that after reduction very small platinum metal particles are present consisting of five to six atoms. CO admission at room temperature leads to complete decomposition of the platinum metal particles and the formation of a platinum carbonyl cluster most probably stabilised by the zeolite walls. Modelling shows that the platinum carbonyl cluster just fits inside the pores of the zeolite-LTL. Analysis of the white line intensities of platinum L_II and L_III X-ray absorption edges reveals that after reduction and in the presence of chemisorbed hydrogen the platinum metal particles in Pt/K-LTL have 0.12% more d-band vacancies than bulk platinum metal. This value increases to 0.34% after CO admission implying-backdonation from platinum to CO, a positive charge on Pt in the newly formed cluster or a combination of both. The results of this study have a large impact on the interpretation of existing literature FTIR CO data obtained on Pt/K-LTL. The results question the validity of CO chemisorption carried out to determine the dispersion of very small platinum particles.     

Different sensory aspects of a food are not remembered with equal acuity

In the present study, food memory for three sensory aspects involved in food perception, taste, texture and aroma, is compared. Participants received a lunch including a custard dessert (target) under incidental learning condition. One day later, participants were presented with samples identical to the target and with distractors varying either in sweetness, thickness or cherry aroma. Memory was assessed by an absolute recognition question (“Did you eat this sample yesterday?”) and by relative questions (“Is this sample less, equal or more sweet than the sample you ate yesterday?”). Results showed better memory performance for sweetness than for the two other sensory aspects, both in the absolute and in the relative tests. Several hypotheses to explain the differences in memory between different sensory aspects of a food are discussed.     

Attenuated total reflection-infrared nanofluidic chip with 71 nL detection volume for in situ spectroscopic analysis of chemical reaction intermediates

We present a micromachined silicon attenuated total reflection-infrared (ATR-IR) crystal with integrated nanofluidic glass channels which enables infrared spectroscopic studies with only 71 nL sample volume. Because of the short path length through silicon, the system allows IR spectroscopy down to 1200 cm(-1), which covers the typical fingerprint region of most organic compounds. To demonstrate proof-of-principle, the chip was used to study a Knoevenagel condensation reaction between malononitrile and p-anisaldehyde catalyzed by different concentrations of 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) in solvent acetonitrile. By in situ measurement, it was demonstrated for the first time that at certain concentrations of DBU, reaction intermediates become stabilized, an effect that slows down or even stops the reaction. This is thought to be caused by increased ionic character of the solvent, in which protonated DBU stabilizes the intermediates. This clearly demonstrates that infrared mechanistic studies of chemical reactions are feasible in volumes as little as 71 nL.     

An atomic X-ray absorption fine structure study of the influence of hydrogen chemisorption and support on the electronic structure of supported Pt particles

The physical principles of atomic XAFS (AXAFS) are presented along with important details on how to isolate the AXAFS contribution from the experimental XAFS data. Intuitive illustrations are given showing how various interactions of the absorber atom with its neighbours influence the AXAFS contribution. Hydrogen chemisorbed on the surface of the supported metal particles is shown to have a strong influence on the amplitude of the Fourier transform AXAFS peak. The effect of the support (with different amounts and types of charge compensating ions (H⁺, K⁺), different Si/Al ratio and extra-framework Al) on the experimental AXAFS spectra of Pt dispersed in zeolites (LTL,Y) and on flat supports (Al₂O₃–SiO₂, MgO–Al₂O₃) are summarised. It is shown that the essence of the metal–support interaction, as revealed in the AXAFS, is a shift in the ionisation potential of the valence d-orbital electrons brought about by the polarisation induced primarily by the changing charge on the support oxygen atoms. This revised version was published online in June 2006 with corrections to the Cover Date.     

Incidental learning and memory for food varied in sweet taste in children

This experiment investigated incidental learning and memory in children (age 7-10 years) for three different foods (fruit juice, fruit purée and biscuit), varied in sweetness. Children (N = 286) were exposed to three target foods and 24 h later their incidental learning was tested for one of the foods by asking them to recognize the target among distractors varying in sweetness. Children were also asked to rate their liking for the products.Overall, the children showed incidental learning for the food eaten the previous day, but recognition was not equal for all stimuli: a memory effect was found for fruit purée but not for biscuit and fruit juice. Memory was based on the correct rejection of the distractors rather than on target recognition. Hedonic scores were high, but lowest for fruit purée. Memory was not related to liking, but it is likely that other factors like novelty and familiarity may have been influential.     

Salt Reduction in Foods Using Naturally Brewed Soy Sauce

ABSTRACT:  In recent years, health concerns related to salt/sodium chloride consumption have caused an increased demand for salt-reduced foods. Consequently, sodium chloride (NaCl) reduction in foods has become an important challenge. The more so, since a decrease in NaCl content is often reported to be associated with a decrease in consumer acceptance. The objective of the present study was to investigate whether or not it would be possible to reduce the NaCl content in standard Western European foods by replacing it with naturally brewed soy sauce. Three types of foods were investigated: salad dressing ( n  = 56), soup ( n  = 52), and stir-fried pork ( n  = 57). In the 1st step, an exchange rate (ER) by which NaCl can be replaced with soy sauce without a significant change in the overall taste intensity was established per product type, by means of alternative forced choice tests. In the 2nd step, the same consumers evaluated 5 samples per product type with varying NaCl and/or soy sauce content on pleasantness and several sensory attributes. The results showed that it was possible to achieve a NaCl reduction in the tested foods of, respectively, 50%, 17%, and 29% without leading to significant losses in either overall taste intensity or product pleasantness. These results suggest that it is possible to replace NaCl in foods with naturally brewed soy sauce without lowering the overall taste intensity and to reduce the total NaCl content in these foods without decreasing their consumer acceptance.
PRACTICAL APPLICATION: Health concerns related to salt consumption cause an increased demand for salt-reduced foods. Consequently, the development of foods with reduced salt content without decreasing the consumer acceptance is an important challenge for the food industry. A new possible salt reduction approach is described in the present article: The replacement of salt with naturally brewed soy sauce.