We have investigated the adsorption and reaction of methanol with Au/TiO2 catalysts using a pulsed flow reactor, DRIFTS and TPD. The TiO2 (P25) surface adsorbed a full monolayer of methanol, much of it in a dissociative manner, forming methoxy groups associated
with the cationic sites, and hydroxyl groups at the anions. The methoxy is relatively stable until 250 °C, at which point
decomposition occurs, producing mainly dimethyl ether by a bimolecular surface reaction. As the concentration of methoxy on
the surface diminishes, so the mechanism reverts to a de-oxygenation pathway, producing mainly methane and water (at ~330 °C
in TPD), but also with some coincident CO and hydrogen. Au catalysts were prepared by the deposition-precipitation method
to give Au loadings between 0.5–3 wt %. The effect of low levels of Au on the reactivity is marked. The pathway which gives
methane, which is characteristic of titania, remains, but a new feature of the reaction is the evolution of CO2 and H2 at lower temperature (a peak is seen in TPD at 220 °C), and the elimination of the DME-producing state. Clearly this is associated
with the presence of Au and appears to be due to the production of a formate species on the surface of the Au component. This
formate species is mainly involved in the reaction of methanol with the Au/TiO2 catalysts which results in a combustion pathway being followed, with complete conversion occurring by ~130 °C. 相似文献
A new series of polymers comprising four terpolymers was synthesized via Mannich polycondensation of benzene-1,4-diamine, formaldehyde and piperazine by varying the benzene-1,4-diamine and piperazine ratio. The new polyamines (labeled Dipip) were characterized using 13C solid-state NMR, FT-IR, TGA, DSC, XRD, SEM and EDX. The adsorptive performances of the synthesized polymers for Erichrome Black T (EBT) uptake from aqueous solution were investigated under batch process. Equilibrium, kinetic, and thermo-dynamic studies were conducted to determine the influence of different operational parameters of the adsorption process. The two most promising polymers among the series show an excellent EBT removal efficiency of~100%and~95%with high adsorption capacities of 775 mg·g- 1 and 917 mg·g- 1, respectively at a meager dosage of 5 mg. The sorption of EBT on the polymers was well described by Redlich-Peterson&Langmuir model while the kinetic studies indicate that pseudo-second order model was followed. For the thermodynamic studies, the negativeΔG and positiveΔH values obtained suggest a spontaneity of the sorption process which was endothermic in nature. The results of reusability test of the resins were promising even at the fourth cycle, showcasing the potentials of the new polymers in dyes contaminated water treatment. 相似文献
Random causes are vital part of every process in manufacturing and nonmanufacturing environments, and these do not affect the product features. Special causes, on the other hand, come because of some burden(s) in a process and requires special attention; otherwise, it ruins the products excellence. Special causes are categorized into small, moderate, and large shifts and are handled by statistical quality control charts. The Shewhart control chart is well known for large shifts, while the cumulative sum and exponentially weighted moving average are more effective in detecting small to moderate shifts. However, in practice, many processes require the simultaneous monitoring of both the small to the large shifts. In this study, we have designed an adaptive EWMA for dispersion parameter in connection with Huber and Tukey's bisquare functions. The performance measures used in this study include average run length, extra quadratic loss, relative average run length, and performance‐comparison index. We have observed that the study proposals are good competitors to the other counter parts for an efficient monitoring of shifts of varying amounts. An illustrative example using real data is given to demonstrate the implementation of the study proposal. 相似文献
Methanol can be reformed with water, at ambient temperature, using photocatalysis, and this reaction represents a possible
low energy, more sustainable pathway to hydrogen production than (for instance) steam reforming. The requirements for the
catalysts are rather strict since titania itself is almost inactive for anaerobic photocatalysis, whereas the addition of
a very limited range of metals to the surface renders it active. Surprisingly, this includes gold, which shows one of the
highest reactivities for hydrogen production. The mechanism is proposed to involve the methoxy and formate intermediates,
the latter being implicated in the route to CO2 and hydrogen production. One oxygen atom is supplied from the titania support, which is replaced in the catalytic cycle by
oxygen from water. The threshold for the excitation is that for bandgap excitation into the titania conduction band, which
stores the energy for reactivation, and this is mediated by electrophilic oxygen. 相似文献
Delayed completion of a construction project is often caused by a complex interaction of a combination of events, some of which are the contractor’s risks and others are the project owner’s. The apportionment of the liability to give effect to the risk allocation has therefore been a matter of great controversy. Many delay analysis methodologies have been developed over the years for performing this task. This paper reports on an empirical study into the current practice in the use of these methodologies in the United Kingdom, as part of a wider study aimed at developing a framework for improving delay claims analysis. The part of the study reported here was based on a questionnaire survey of key informants. The issues investigated include the categories of staff within contracting organizations who contribute to delay claims analyses, the awareness, use and reliability of existing delay analysis methods and the obstacles to their use in practice. The main findings of the study are that: (1) the preparation of delay claims often requires input from commercial managers (quantity surveyors), schedulers, site managers, external claim consultants and estimators; (2) commercial managers have the greatest involvement; (3) claims analyzed using the as-built versus as-planned and the impacted as-planned techniques are often successful although there is considerable literature on the shortcomings of these techniques; and (4) the main obstacles to the use of the methods relates to deficiencies in project records and scheduling practice. 相似文献
It is generally thought that catalysts produced by incipient wetness impregnation (IW) are very poor for low temperature CO oxidation, and that it is necessary to use methods such as deposition–precipitation (DP) to make high activity materials. The former is true, indeed such IW catalysts are poor, and we present reactor data, XPS and TEM analysis which show that this is due to the very negative effect of the chloride anion involved in the preparation, which results in poisoning and excessive sintering of the Au particles. With the DP method, the chloride is largely removed during the preparation and so poisoning and sintering are avoided.
However, we show here that, contrary to previous considerations, high activity catalysts can indeed be prepared by the incipient wetness method, if care is taken to remove the chloride ion during the process. This is achieved by using the double impregnation method (DIM). In this a double impregnation of chloroauric acid and a base are made to precipitate out gold hydroxide within the pores of the catalyst, followed by limited washing. This results in a much more active catalyst, which is active for CO oxidation at ambient temperature. The results for DIM and DP are compared, and it is proposed that the DIM method may represent an environmentally and economically more favorable route to high activity gold catalyst production. 相似文献