Treatment of montmorillonite and vermiculite with hydrochloric acid results in an overall increase in acidity and acidic sites. IR and DSC studies of base adsorbed catalysts have revealed the heterogeneity of surface acidity on the activated catalysts. Clay catalysts have been found to dehydrate 1-butanol to 1-butene, which directly isomerizes tocis- andtrans-2-butenes, confirming the presence of Lewis and Brönsted acid sites. Cumene cracking studies using the clay catalyst also confirm the presence of Brönsted acid sites. The temperature and concentration of acid have been found to have a significant influence on the catalytic activity. 相似文献
The adsorption and desorption of n-hexane over Zeolite-5A has been investigated as a function of loading using simultaneous Fourier transform infrared (FTIR)-temperature-programmed desorption (TPD) measurements. The TPD profiles show a second peak developing at lower temperatures when loading exceeds 16 hexane molecules per Zeolite-5A unit cell or two molecules per alpha-cavity of the Zeolite-5A structure. The infrared spectra rule out two types of adsorption sites as the origin of the two peaks in the TPD. Changes in the conformation of the adsorbed hexane as a function of loading and temperature were followed by monitoring the position of the methylene stretching modes in the infrared spectra. With increasing loading, the adsorbed hexane adopts a stretched trans conformation. These changes occur at loading levels below 12 hexane molecules per Zeolite-5A unit cell. No change is observed above this loading, ruling out any conformational change at loadings where the second peak is seen in the TPD. The second peak in the TPD arises, therefore, from a combination of steric repulsion and loss of translational entropy. 相似文献
Thermal investigations of two novel coordination compounds, potential precursor of copper sulfides, namely [Cu2(S2O3)2(NH3)4]·5H2O and Na2[Cu4(S2O3)5(NH3)8]·2H2O were performed either in solid state (static air atmosphere), as well as in reaction medium. During both decompositions,
Cu2+ reduction occurs. In solid state decomposition, a mixture containing sulfides and sulfates is observed. In the reaction medium,
CuSy compounds with sulfur content y (0.66<y<1) dependent on thiosulfate concentration are obtained.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
The use of recorded lecture videos (RLVs) in mathematics instruction continues to advance. Prior research at the post-secondary level has indicated a tendency for RLV use in mathematics to be negatively correlated with academic performance, although it is unclear whether this is because regular users are generally weaker mathematics students or because RLV use is somehow depressing student learning. Through the lens of cognitive engagement, a quasi-experimental pre- and post-test design study was conducted to investigate the latter possibility.
Cognitive engagement was operationalized using the Revised Two-Factor Study Process Questionnaire (R-SPQ-2F), which measures learning approaches on two major scales: surface and deep. In two mathematics courses at two universities, in Australia and the UK, participants were administered the questionnaire near the course start and finish. Overall findings were similar in both contexts: a reduction in live lecture attendance coupled with a dependence on RLVs was associated with an increase in surface approaches to learning.
This study has important implications for future pedagogical development and adds to the sense of urgency regarding research into best practices using RLVs in mathematics. 相似文献
The present study was undertaken to examine if a subject's voice F0 responded not only to perturbations in pitch of voice feedback but also to changes in pitch of a side tone presented congruent with voice feedback. Small magnitude brief duration perturbations in pitch of voice or tone auditory feedback were randomly introduced during sustained vowel phonations. Results demonstrated a higher rate and larger magnitude of voice F0 responses to changes in pitch of the voice compared with a triangular-shaped tone (experiment 1) or a pure tone (experiment 2). However, response latencies did not differ across voice or tone conditions. Data suggest that subjects responded to the change in F0 rather than harmonic frequencies of auditory feedback because voice F0 response prevalence, magnitude, or latency did not statistically differ across triangular-shaped tone or pure-tone feedback. Results indicate the audio-vocal system is sensitive to the change in pitch of a variety of sounds, which may represent a flexible system capable of adapting to changes in the subject's voice. However, lower prevalence and smaller responses to tone pitch-shifted signals suggest that the audio-vocal system may resist changes to the pitch of other environmental sounds when voice feedback is present. 相似文献
Si was deposited on the glass substrate as an interlayer for the 2-D growth of Ag thin films because Si has a strong binding energy against Ag and can lead to a negative surface energy change in Ag/glass. The Si interlayer induced an extremely smooth and flat Ag surface, which effectively reduced the resistance and enhanced the reflectance in the IR region. In particular, Ag (9 nm)/Si (3 nm)/glass showed 0.074 emissivity and ∼91% reflectance in the IR region with 67% transmittance in the visible region. 相似文献