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Effect of pretreatment conditions on the catalytic performance of Ni-Pt-W supported on amorphous silica-alumina catalysts: Part 2. Catalysts prepared by a hybrid method

Paper ID Volume ID Publish Year Pages File Format Full-Text
43695 45983 2008 12 PDF Available
Title
Effect of pretreatment conditions on the catalytic performance of Ni-Pt-W supported on amorphous silica-alumina catalysts: Part 2. Catalysts prepared by a hybrid method
Abstract

Activation procedures of Ni-W-Pt based catalysts, prepared by means of a hybrid technique: sol–gel and incipient wetness impregnation, were investigated in terms of their activity in reaction of n-hexane isomerization in a continuous fixed-bed quartz reactor operating at atmospheric pressure, by changing operating conditions such as time on stream, SiO2/Al2O3 and H2/n-hexane ratios. This study aims to understand the effects of the pretreatment conditions, such as calcination and reduction temperature, over some properties of these catalysts and to analyze the relationship between the metal content, the acidity (strength) of the samples and their catalytic performance.The chemical composition of the prepared solids have bas characterized by inductively coupled plasma-atomic emission spectroscopy (ICP-AES), their specific surface areas were measured using BET method, while their reduction behavior was characterized by temperature-programmed reduction and their acidity was assessed by means of ammonia temperature-programmed desorption. The collected data revealed that both BET surface areas and catalytic activity as well as surface acidity of these solids are strongly dependent on their pretreatment conditions. Besides, the reduction behavior of the prepared materials was related to nickel and platinum amounts, the higher the concentrations of these species the easier the reducibility of the samples. On the other hand, it was found that all (NixPty) catalysts deactivate with time on stream, with the conversion remaining steady after 100 min. Moreover, the obtained results on (Ni12Pt0,4)AC catalyst showed that the SiO2/Al2O3 ratio and H2 partial pressure affect isomerization selectivity positively while opposite effect was observed for activity (conversion). In addition, the main products in n-hexane hydroconversion were found to be monobranched isomers which dominate all practical conversions and their formation increases together with that of multibranched ones. Besides, the cracked products are not produced in significant amounts until about 30% conversion.

Graphical abstractActivation procedures of Ni-W-Pt based catalysts, prepared by means of an hybrid technique: sol–gel and incipient wetness impregnation, were investigated in terms of their activity in reaction of n-hexane isomerization in a continuous fixed-bed quartz reactor operating at atmospheric pressure, by changing operating conditions such as time on stream, SiO2/Al2O3 and H2/n-hexane ratios. This study aims to understand the effects of the pretreatment conditions, such as calcination and reduction temperature, over some properties of these catalysts and to analyze the relationship between the metal content, the acidity (strength) of the samples and their catalytic performance.The chemical composition of the prepared solids have been characterized by inductively coupled plasma-atomic emission spectroscopy (ICP-AES), their specific surface areas were measured using BET method, while their reduction behavior was characterized by temperature-programmed reduction and their acidity was assessed by means of ammonia temperature-programmed desorption. The collected data revealed that both BET surface areas and catalytic activity as well as surface acidity of these solids are strongly dependent on their pretreatment conditions. Besides, the reduction behavior of the prepared materials was related to nickel and platinum amounts, the higher the concentrations of these species the easier the reducibility of the samples. On the other hand, it was found that all (NixPty) catalysts deactivate with time on stream, with the conversion remaining steady after 100 min. Moreover, the obtained results on (Ni12Pt0,4)AC catalyst showed that the SiO2/Al2O3 ratio and H2 partial pressure affect isomerization selectivity while positively opposite effect was observed for activity (conversion). In addition, the main products in n-hexane hydroconversion were found to be monobranched isomers which dominate all practical conversions and their formation increases together with that of multibranched ones. Besides, the cracked products are not produced in significant amounts until about 30% conversion. Figure optionsDownload full-size imageDownload as PowerPoint slide

Keywords
Platinum; Tungsten-oxide; Nickel; Isomerization; Pretreatment conditions; Hybrid technique
First Page Preview
Effect of pretreatment conditions on the catalytic performance of Ni-Pt-W supported on amorphous silica-alumina catalysts: Part 2. Catalysts prepared by a hybrid method
Publisher
Database: Elsevier - ScienceDirect
Journal: Applied Catalysis A: General - Volume 345, Issue 2, 1 August 2008, Pages 164–175
Authors
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Subjects
Physical Sciences and Engineering Chemical Engineering Catalysis