Investigation of Ceria Supported Palladium Catalysts for Selective Hydrogenation of Acetylene in Ethylene PDF Download
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Author: Junyi He
Publisher:
ISBN:
Category : Chemistry
Languages : en
Pages : 114
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Author: Junyi He
Publisher:
ISBN:
Category : Chemistry
Languages : en
Pages : 114
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Author: Tengteng Lyu
Publisher:
ISBN:
Category : Chemistry
Languages : en
Pages : 128
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Author: Wentao Xie
Publisher:
ISBN:
Category : Chemical engineering
Languages : en
Pages : 124
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Author: Ruijun Hou
Publisher: Springer
ISBN: 981100773X
Category : Science
Languages : en
Pages : 151
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This thesis offers novel methods for catalyst and process design for the selective hydrogenation of acetylene and 1,3-butadiene. The author predicts the properties of supported Pd–Ni bimetallic catalysts using density functional theory (DFT) calculations and temperature-programmed desorption (TPD). The excellent correlation between model surfaces and supported catalysts demonstrates the feasibility of designing effective bimetallic catalysts for selective hydrogenation reactions. The author also proposes a method for designing non-precious metal catalysts to replace precious metals. She modifies the process of selective hydrogenation of acetylene by coupling the selective adsorption to the selective hydrogenation in the liquid phase, as a result of which the ethylene selectivity is greatly improved and heat transfer is greatly enhanced. Lastly, by analyzing the mechanism of liquid-phase hydrogenation, the author proposes a multi-stage slurry bed reactor for industrial applications.“/p>
Author:
Publisher:
ISBN:
Category : Acetylene
Languages : en
Pages : 190
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In this study, the effects of alumina grinding and mixed oxides (ZnO-Al2O3 and NiO-Al2O3) grinding with various Zn/Al and Ni/Al molar ratios (0.1 and 0.5) prepared by an attrition ball mill on catalytic performance of alumina supported Pd catalysts for selective hydrogenation of acetylene were investigated. It was found that catalytic performances of the Pd catalyst supported on Al2O3 milled for 12 h were superior compared to those of Pd-supported on the unmilled Al2O3. However, all the catalysts prepared from milled mixed oxides presented lower acetylene conversion and ethylene selectivity than that of the catalyst prepared from alumina milled for 12 h. From X-ray diffraction, it was suggested that varying milling time directly affected the crystallite size, surface area and acidity of alumina supports. As revealed by CO chemisorption, milling of Al2O3 supports could increase metal active sites of Pd/Al2O3 catalysts without change in the interaction between Pd and the alumina support so that the catalysts exhibited higher acetylene activity and ethylene selectivity. Moreover, increasing of acidity affected coke formation on the catalysts.
Author: Ying Ji
Publisher:
ISBN:
Category : Acetylene
Languages : en
Pages : 94
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Author: Luis Fabián Peña-Orduña
Publisher:
ISBN:
Category : Acetylene
Languages : en
Pages : 92
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Author: Seraj Saleh Albanoon
Publisher:
ISBN:
Category : Acetylene
Languages : en
Pages : 162
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Author:
Publisher:
ISBN:
Category : Palladium
Languages : en
Pages : 310
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The performance of supported palladium catalysts that had been modified with triphenyl phosphine, diphenyl sulfide and triphenyl amine was compared to unmodified Pd/TiO2 catalysts. It was found that the selectivity was superior to the unmodified catalysts with or without the use of carbon monoxide as a modifier. Ethylene selectivities in excess of 70 % at conversion levels greater than 80% were observed on the modified catalysts under conditions of excess hydrogen which compares extremely well with other catalysts found in the literature. The modifier was found to significantly reduce the number of high energy sites on the surface on the palladium, thereby significantly hindering ethylene hydrogenation but not affecting acetylene hydrogenation. The simple preparation of these catalysts together with the simplicity added by not having to use carbon monoxide or limited hydrogen promises a viable alternative strategy for commercial catalysis.
Author: Anish Dasgupta
Publisher:
ISBN:
Category :
Languages : en
Pages :
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Intermetallic compounds often offer opportunities for synthesis of site isolated catalysts having precise active site coordination and morphology. They are also resistant to segregation effects (compared to random alloys) because of the high heat of formation of their unique electronically stabilized crystal structures. Due to predictable, periodic and easily reproducible nature of the isolated active sites, suitably chosen intermetallic compounds can act as excellent model systems for studying catalytic structure function correlation in different small molecule chemistries. In the current dissertation I utilized H2-D2 exchange in addition to ethylene and acetylene hydrogenation as the probe reactions of choice. My ultimate target is to understand and quantify the effect of active site (transition metal) isolation during the semi-hydrogenation of acetylene in an ethylene rich stream, which is a key step in industrial polyethylene synthesisa multi-hundred-billion-dollar industry. I studied two different classes of catalysts for this chemistry: Pd-(M)-Zn (M=Cu, Ag, Au) -brass intermetallics and Ni-Ga intermetallics. I used micron scale bulk materials as model catalysts because they provide greater compositional control and allows for studying the intrinsic catalytic property of the intermetallic, free from support and ligand effects.A significant part of the text is dedicated to the synthesis, characterization and catalytic study of the bulk Pd-(M)-Zn ternary -brass phase materials because of its unique adaptability in terms of developing a family of closely related model catalysts having Pd-M-Pd active sites (M=Pd, Zn, Au, Cu and Ag) which can change the semi-hydrogenation activity and selectivity by two orders of magnitude even when only one atom is changed per 52 atom unit cell. As an extension of this project I also report several Pd-Ni-Zn and Pd-Pt-Zn ternary -brass phases and determine their atomic site occupancy factors.During the course of my research I realized there were no reported methods for synthesizing Pd-Zn and Ni-Zn -brass intermetallics as catalytically relevant supported nano-particles (NPs). I developed and optimized a hybrid generalized synthesis approach for SiO2 supported Pd-Zn, Ni-Zn and Cu-Zn -brass NPs. I also provide preliminary evidence that this approach can be easily extended to the synthesis of ternary NPs as well.In the case of Ni-Ga intermetallics, I tried to understand the role of Ga in controlling acetylene semi-hydrogenation. I observed a reversal in the ethylene selectivity trend with Ga content between 85 C and 160 C which is unexpected based on published DFT calculations. Previously, it has been suggested that Ga simply acts as a spacer for isolating Ni/Pd active sites much like Zn in the case of Ni-Zn catalysts (studied by Charles Spanjers from our research group). However, Ga has a higher affinity to hydrogen compared to Zn and I attempted to investigate if Ga may have a weak but non-negligible catalytic contribution towards hydrogenation which has typically not been previously considered in any detail in the case of acetylene semi-hydrogenation on metallic catalysts. Additionally, I provide understanding behind the high acetylene semi-hydrogenation selectivity of Ni5Zn21 catalyst which was originally reported by Spanjers et al. (J. Catal. 2014). This involved identifying the site occupation factor of Ni and Zn in the -brass lattice for materials having greater than 15.4 at% Ni. It is determined that (unlike Pd-Zn -brass) exactly single atom Ni1 active sites are exposed on the surface irrespective of the Ni concentration (even though Ni3 clusters are present in the bulk) which explains the suppression of over-hydrogenation and oligomerization on this catalyst, resulting in the high ethylene selectivity reported by Spanjers et al.
