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    DFT Investigation of the catalytic conversion of acetic acid to acetone on the zeolite H-ZSM5
    (2022-12-01)
    Konsue, Adchatawut
    ;
    Gleeson, M. Paul
    ;
    Gleeson, Duangkamol
    Biomaterials processing has become increasingly important in the chemical industry. Identification and optimization of processes to facilitate biomass conversion is therefore recognized as being of great importance. Carboxylic acids derived from biomaterials are important building blocks that can be used in a wide variety of industrial applications. As such, methods to process them in an efficient and cost-effective manner are highly desirable. In this study we report the use of theoretical methods to explore the catalytic conversion of acetic acid to acetone on the zeolite H-ZSM5. We have employed a 46T DFT cluster model to explore mechanistic proposals reported in the literature. We investigate the relative energetics associated with the formation of the proposed intermediates, including acyl-zeolite complexes, enols, acylium cations, ketenes, anhydrides, and beta-keto acids, that could potentially connect acetic acid to the desired product, acetone. This assessment would allow us to identify the most probable mechanism connecting the reactant to products. We predict a low energy pathway starting with the generation of a surface acyl, followed by an anhydride, with the rate determining step involving methyl group migration. The reaction is predicted to be bi-molecular and involves C-C bond formation, in line with proposals based on isotopic labelling experiments.
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    Methanol dehydration to dimethyl ether over strong-acid-modified diatomite catalysts
    (2016-11-01)
    Pranee, Watcharakorn
    ;
    Neramittagapong, Sutasinee
    ;
    Assawasaengrat, Pornsawan
    ;
    Neramittagapong, Arthit
    Dimethyl ether synthesis via methanol dehydration over strong-acid-modified (with sulfuric, hydrochloric and nitric acid) diatomite (DM) catalysts was conducted in a fixed-bed reactor with elevated temperature reaction from 250 to 350°C. The modified DM catalysts were characterized by using X-ray diffraction, scanning electron microscopy, fourier transform infrared spectroscopy, fourier transform Raman spectroscopy, temperature-programmed desorption of ammonia, temperature-programmed of carbon dioxide, thermal gravimetric analysis, and solid-state 27Aluminum magic angle spinning/nuclear magnetic resonance spectroscopy. It was found that sulfuric-acid-modified DM catalyst yielded the highest DME selectivity (~99%). It was also revealed that methanol conversion depended on Al ions. The methanol conversion increased with Al<sup>(IV)</sup> but decreased with Al<sup>(V)</sup> and Al<sup>(VI)</sup>.
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    Dimethyl ether synthesis from methanol over diatomite catalyst modified using nitric acid treatment
    (2016-08-02)
    Pranee, Watcharakorn
    ;
    Neramittagapong, Sutasinee
    ;
    Assawasaengrat, Pornsawan
    ;
    Neramittagapong, Arthit
    Dimethyl ether synthesis from methanol over diatomite catalysts modified using nitric acid was investigated. The catalytic performance of diatomite was tested in a fixed-bed reactor under atmospheric pressure and within the temperature range of 250–350°C. It was discovered that high acidity of the catalyst yielded a higher methanol conversion rate. Moreover, it was revealed that the acidity of the catalyst surface was controlled by Al<sup>(IV)</sup> ions whereas basicity of the catalyst surface was determined by Al<sup>(V)</sup> and Al<sup>(VI)</sup> ions. From this finding, the authors were able to propose the mechanism of DME synthesis from methanol over treated diatomite.
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    Dimethyl ether synthesis via methanol dehydration over BEA zeolite from bagasse fly ash with zircronium- and nickel-ion exchange
    (2014-01-01)
    Pranee, Watcharakorn
    ;
    Assawasaengrat, Pornsawan
    ;
    Neramittagapong, Arthit
    ;
    Intarachit, Sasitorn
    ;
    Neramittagapong, Sutasinee
    The synthesis of dimethyl ether via methanol dehydration has been carried out over Beta zeolite (BEA) and ion-exchanged Beta zeolite from bagasse fly ash using hydrothermal method. The reactions were taken place in a fixed-bed reactor. The effects of nickel and zirconium ionexchanged of BEA were investigated. Ni-BEA zeolite exhibited high methanol conversion rate and DME-resultant upon the reaction temperature from 200 to 225°C with equilibrium-limiting condition over 225°C; Furthermore, the Ni-BEA zeolite presented the best stable activity at 225°C over 1,200 minute. The Ni-BEA zeolite has also been interesting as a zeolite which suited to be one role importance to improve the properties for methanol dehydration to dimethyl ether. © (2014) Trans Tech Publications, Switzerland.
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    Dimethyl ether synthesis via methanol dehydration over diatomite catalyst modified using hydrochloric acid
    (2014-01-01)
    Pranee, Watcharakorn
    ;
    Assawasaengrat, Pornsawan
    ;
    Neramittagapong, Arthit
    ;
    Neramittagapong, Sutasinee
    The synthesis of dimethyl ether via methanol dehydration has been carried out over untreated-diatomite catalyst (DM) and hydrochloric acid modified treatment on diatomite catalyst (DMHC). The reactions were carried out in a fixed-bed reactor. The effects of hydrochloric acid modifications of diatomite on its catalytic performance were studied. The characterization such as XRD, SEM, FT-IR and FT-Raman had no deformation after HCl-modified treatment on catalysts. DMHC catalyst apparently gave the higher methanol conversion rate than DM due to the acidity while the selectivity of dimethyl ether from 250 to 350°C was slightly changed. The acidity was depended upon Al<sup>(IV)</sup> ions; nevertheless, both Al<sup>(V)</sup> and Al<sup>(VI)</sup> were affected and hence increasing the basic active sites. Not only was the competitively catalytic methanol dehydrogenation preferred with basic condition but also methanol-blocking water molecule interaction was the unwanted reaction. In this investigation, the chemical-bond arrangements of silicon and aluminium ions were proposed with solid MAS/NMR. The DMHC catalyst exhibited better DME yield than the DM catalyst, and it could be used as a selective catalyst for DME synthesis from methanol. © (2014) Trans Tech Publications, Switzerland.