• Korean Chemical Engineering Research
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• v.50 no.2
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• pp.251-256
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• 2012

Etherification of n-butanol to di-n-Butyl Ether was carried out over Keggin $H_{3+x}PW_{12-x}Nb_xO_{40}$ (x=0, 1, 2, 3) and $H_{6+x}P_2W_{18-x}Nb_xO_{62}$ (x=0, 1, 2, 3) Wells-Dawson heteropolyacid catalysts. Niobium-substituted Keggin and Wells-Dawson heteropolyacid catalysts with different niobium content were prepared. Successful preparation of the catalysts was confirmed by FT-IR, ICP-AES, and $^{31}P$ NMR analyses. Their acid properties were determined by $NH_3$-TPD (Temperature-Programmed Desorption) measurements. Heteropolyacid catalysts showed different acid properties depending on niobium content in both series. The correlation between acid properties of heteropolyacid catalysts and catalytic activity was then established. Acidity of Keggin and Wells-Dawson heteropolyacid catalysts decreased with increasing niobium content, and conversion of n-butanol and yield for di-n-butyl ether increased with increasing acidity of the catalysts, regardless of the identity of heteropolyacid catalysts (without heteropolyacid structural sensitivity). Thus, acidity of heteropolyacid catalysts served as an important factor determining the catalytic performance in the etherification of n-butanol to di-n-Butyl Ether.

• Clean Technology
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• v.16 no.3
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• pp.220-228
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• 2010

Four Keggin-type heteropolyacids, $H_nXM_{12}O_{40}$(X = P and Si, M = W and Mo) that were substituted with heteroatom and polyatom were applied to the dehydration reaction of fructose to 5-hydroxymethylfurfural (HMF). The results showed that the acid became stronger when the heteroatom and polyatom were substituted with P and W than the cases of Si and Mo, respectively. However, the amount of acidic sites increased with the decrease in the acid strength, resulting in the change of the catalytic activity of heteropolyacids in the dehydration reaction. The experimental results revealed that four different heteropolyacids produced similar amounts of HMF via the dehydration reaction of fructose due to the counterbalancing effect between the amount of active sites, which is related to the catalytic activity of heteropolyacids, and the softness of polyanion. In addition, it was observed that the prepared heteropolyacids showed good structural stability after heat treatment at $200^{\circ}C$.

• Clean Technology
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• v.25 no.1
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• pp.91-97
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• 2019

Oxidative desulfurization (ODS) has received much attention in recent years because refractory sulfur compounds such as dibenzothiophenes can be oxidized selectively to their corresponding sulfoxides and sulfones, and these products can be removed by extraction and adsorption. In this work, The oxidative desulfurization of marine diesel fuel was performed in a batch reactor with hydrogen peroxide ($H_2O_2$) in the presence of various supported heteropoly acid catalysts. The catalysts were characterized by XRD, XRF, XPS and nitrogen adsorption isotherm techniques. Based on the sulfur removal efficiency of promising silica supported heteropoly acid catalysts, the ranking of catalytic activity was: $30\;H_3PW_{12}/SiO_2$ > $30\;H_3PMo_{12}/SiO_2$ > $30\;H_4SiW_{12}/SiO_2$, which appears to be related with their intrinsic acid strength. The $30\;H_3PW_{12}/SiO_2$ catalyst showed the highest initial sulfur removal efficiency of about 66% under reaction conditions of $30^{\circ}C$, $0.025g\;mL^{-1}$ (cat./oil), 1 h reaction time. However, through the recycle test of the $H_3PW_{12}/SiO_2$ catalyst, significant deactivation was observed, which was attributed to the elution of the active component $H_3PW_{12}$. By introducing cesium cation ($Cs^+$) into the $H_3PW_{12}/SiO_2$ catalyst, the stability of the catalyst was improved with changing the solubility, and the $Cs^+$ ion exchanged catalyst could be recycled for at least five times without severe elution.