Stoichiometric hydrogenation of ethene on Rh(111); mechanism,importance of weakly adsorbed ethene,and relationship to homogeneous catalysis

The hydrogenation of ethene is an important reaction in heterogeneous catalysis and, despite its apparent simplicity, many aspects of the reaction mechanism remain unclear. By contrast, the mechanism using homogeneous catalysts such as Wilkinson's catalyst [(RhCl(PPh₃)₃] is thought to be well understood. To allow a comparison between the homogeneous and heterogeneous reactions we have studied ethene/hydrogen interactions on the (111) plane of rhodium in the temperature range 160–500 K. Under UHV conditions no catalytic reaction was detected. However, we have been able to observe stoichiometric hydrogenation and exchange in the chemisorbed layer. A mixed adlayer of either ethene/deuterium (or perdeuteroethene and hydrogen) was formed at ca. 160 K, and allowed to warm up. From previous spectroscopic studies, ethene is adsorbed at 165 K as partially rehybridised, bonded species with a C-C bond order of ca. 1.5, similar to ethene in Zeise's salt. At 190–210 K we observe coincident desorption of undeuterated ethene — the major species — together with much smaller quantities of deuterated ethane and partially deuterated ethenes. The influence of both hydrogen and ethene pre-coverage has been studied as has the relative extent of hydrogenation and exchange. The ethane formation results parallel those reported by other authors on Pd(110) and Pt(111) and Pt(110). We propose that on all three metals both hydrogenation and exchange follow the same pathway, with a common intermediate for exchange and hydrogenation. This isa weakly held, bonded species formed during the desorption process, which can be convertedreversibly into an adsorbed ethyl species. A detailed comparison indicates that the mechanism of heterogeneous hydrogenation closely parallels that in the homogeneous phase.     

Surface Segregation in Iron Molybdate Catalysts

The high selectivity of iron molybdate catalysts for the production of formaldehyde from methanol is somewhat surprising in view of the very different behaviour of the individual oxides of Fe and Mo for this reaction. The former, on its own, is a complete combustor of methanol, whereas the latter is highly selective. Here we use STEM (scanning transmission electron microscopy) at high resolution to image the surface of small particles of the catalyst and to show that this high selectivity is due to the dominance of the surface region by molybdenum oxide.     

Microstructure alterations in beef intramuscular connective tissue caused by hydrodynamic pressure processing

Scanning electron microscopy (SEM) was utilized to evaluate microstructural changes in intramuscular connective tissue of beef semimembranosus muscle subjected to hydrodynamic pressure processing (HDP). Samples were HDP treated in a plastic container (HDP-PC) or a steel commercial unit (HDP-CU). Control and HDP samples were obtained immediately post-treatment and after 14 days of aging for SEM and Warner–Bratzler shear force (WBSF) analysis. Immediately post-treatment, HDP treated samples exhibited lower (P < 0.01) WBSF than did controls. After aging, HDP-PC samples had lower (P < 0.01) WBSF than that of aged controls. SEM analysis indicated that HDP-PC treatment disrupted the integrity of the collagen fibril network of the endomysium in both the non-aged and aged samples. Aging effects on the intramuscular connective tissue were observed in the HDP-PC and control samples. Both WBSF and connective tissue changes were greater in the HDP-PC than in the HDP-CU treated samples. Data suggest that shockwave alterations to connective tissue contribute to the meat tenderization of HDP.     

Aggressive versus withdrawn unpopular children: variations in peer and self-perceptions in multiple domains

The present study examines whether subgroups of unpopular children differ in terms of competence in multiple domains. Specifically, subgroups of aggressive unpopular, withdrawn unpopular, and aggressive-withdrawn unpopular and average status children were identified on the basis of peer evaluations. The subgroups were then compared in terms of peer and self-perceptions of competence in various nonsocial and social domains. Results indicated that the 3 subgroups of unpopular children exhibited distinct profiles according to peer perceptions, with aggressive-withdrawn unpopular children being viewed as deficient in virtually every area assessed, and aggressive unpopular and withdrawn unpopular children viewed as exhibiting particular strengths and weaknesses across domains. In terms of self-perceptions, results indicated that withdrawn-unpopular children expressed more accurate, but negative self-evaluations, while children in the aggressive subgroups tended to overestimate their competencies.     

CO Spillover and Oxidation on Pt/TiO2

The adsorption of CO has been measured on a 2.5 wt% Pt/TiO₂ catalyst using TPD. A somewhat surprising observation is that (i) CO₂ is produced, even though oxygen is not dosed into the system, (ii) repeated experiments result in the same amount of CO₂ desorption. The results appear to be due to a combination of factors–(i) is due to spillover of CO from the Pt to the TiO₂ support, while (ii) is due to the diffusion of Ti³⁺ into the bulk of the TiO₂ crystallite, which effectively removes the surface non-stoichiometry which might otherwise be expected.     

Effect of Hydrodynamic Pressure Processing on the Processing and Quality Characteristics of Moisture-Enhanced Pork Loins

ABSTRACT: The objective of this study was to determine the influence of hydrodynamic pressure processing (HDP) and aging on the processing characteristics and final meat quality of moisture-enhanced pork loins. Boneless pork loins (n = 24) were split into 3 portions and assigned treatments: control (non-HDP treated, brine-injected), HDP treated before brine-injection, or HDP treated after brine-injection. Pork loins were injected with a salt/phosphate/water solution to 110% of original weight on day 0, intermittently tumbled 3 h, and then held overnight. Meat quality and protein characteristics were measured on days 1 and 8. HDP-treated loins had greater (P < 0.05) brine retention after overnight equilibration and a higher (P < 0.05) processing yield than controls. Warner–Bratzler shear force and expressible moisture decreased (P < 0.0001) with aging from days 1 to 8, but were not significantly affected by either HDP treatment. When the drip loss data from HDP treatments were pooled, HDP samples had lower drip loss values than controls. L* and b* measurements exhibited significant HDP by aging interaction effects, but a* was not influenced by either HDP or aging. Myofibrillar protein solubility and gel electrophoresis measurements of protein degradation were influenced by aging treatments. Data from this study suggest that HDP may have beneficial effects on the processing and final product quality of moisture-enhanced pork loins. Practical Application: This study demonstrates that hydrodynamic pressure processing (HDP) is an effective postharvest technology for improving the processing and meat quality characteristics of moisture-enhanced pork loin products, benefiting both meat processors and consumers.     

Structure sensitivity in CO oxidation over rhodium

The rates of CO oxidation on the (110) and (111) planes of rhodium have been directly compared using a thermal molecular beam reactor. When the surfaces are largely covered by CO the reaction rate is the same on the two crystal planes. At higher temperatures, where CO desorbs and the surface becomes oxygen covered, the reaction becomes structure sensitive, being markedly faster on the more open (110) plane.     

Direct synthesis of formate from methanol oxidation on the CuPd[85∶15]{110}p(2×1) surface: induction of a new reaction pathway via a ligand effect

Thermal molecular beam studies of the oxidative dehydrogenation of methanol over the 1/4 ML and 1/2 ML oxygen predosed CuPd[85 15]{110}p(2 × 1) surfaces has been performed. Post reaction thermal desorption spectroscopy (TDS) clearly shows that during these experiments observable levels of formate are produced. This is in contrast to the results of similar experiments performed over oxidised Cu{110} surfaces which showed little formate production. It is hypothesised that the alloying in the surface region causes this new reaction pathway to appear as a consequence of a modification of the stability of one or more of the reactive intermediates produced in this reaction. It is proposed that these modifications of adsorbate stability are due to a ligand effect arising from the presence of Pd in the second layer of the selvedge.