Synthesis of Mesoporous Metal Oxides by Structure Replication: Thermal Analysis of Metal Nitrates in Porous Carbon Matrices

Christian Weinberger,Jan Hanss,Michael Tiemann,Jan Roggenbuck

doi:10.3390/nano5031431

Christian Weinberger, Jan Hanss + Show 2 more

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https://doi.org/10.3390/nano5031431

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Abstract

A variety of metal nitrates were filled into the pores of an ordered mesoporous CMK-3 carbon matrix by solution-based impregnation. Thermal conversion of the metal nitrates into the respective metal oxides, and subsequent removal of the carbon matrix by thermal combustion, provides a versatile means to prepare mesoporous metal oxides (so-called nanocasting). This study aims to monitor the thermally induced processes by thermogravimetric analysis (TGA), coupled with mass ion detection (MS). The highly dispersed metal nitrates in the pores of the carbon matrix tend to react to the respective metal oxides at lower temperature than reported in the literature for pure, i.e., carbon-free, metal nitrates. The subsequent thermal combustion of the CMK-3 carbon matrix also occurs at lower temperature, which is explained by a catalytic effect of the metal oxides present in the pores. This catalytic effect is particularly strong for oxides of redox active metals, such as transition group VII and VIII metals (Mn, Fe, Co, Ni), Cu, and Ce.

Highlights

Nanocasting is a well-established method of preparing ordered, mesoporous materials, such as mesoporous carbon, metals or metal oxides [1,2,3,4,5,6,7,8]
The thermal combustion of the CMK-3 carbon occurs at a temperature between ca. 450 °C and 610 °C
The thermally induced conversion of metal nitrates into the respective metal oxides inside the pores a mesoporous CMK-3 carbon matrix and the subsequent thermal combustion of the carbon matrix has previously shown to provide a versatile means of preparing mesoporous metal oxides

Summary

Introduction

Nanocasting is a well-established method of preparing ordered, mesoporous materials, such as mesoporous carbon, metals or metal oxides [1,2,3,4,5,6,7,8]. A mesoporous silica material serves as a structure matrix. Its pores are filled with a precursor compound for the desired product, e.g., sucrose [9] or other carbonic species [10,11] for porous carbon, or metal nitrates for metal oxides [5,6,7]. The precursor is converted into the respective product inside the silica pores. The product can be envisaged as a “negative replica” of the silica matrix

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