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Title: Understanding the chemistry of small pore SAPO materials for emissions control applications
Author: Ansari, Zarrin
ISNI:       0000 0004 7228 7469
Awarding Body: UCL (University College London)
Current Institution: University College London (University of London)
Date of Award: 2017
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The work described in this thesis focusses on the hydrothermal synthesis and characterisation of silicoaluminophosphates (SAPOs) as solid state heterogeneous catalyst supports. Various synthesis strategies were explored to observe structural formation and to identify features that enhance the stability and catalytic activity of copper activated small pore SAPOs for ammonia selective catalytic reduction (SCR) in auto-exhaust applications. The primary characterisation techniques used include X-ray diffraction (XRD), solid state nuclear magnetic resonance (SSNMR), X-ray photoelectron spectroscopy (XPS) and inductively coupled plasma mass spectroscopy (ICP MS). The crystallisation process of SAPO-34 (CHA) was investigated using tetraethylammonium hydroxide (TEAOH) as the structure directing additive (SDA) with two reactant gel compositions of varying silica concentration to determine the speciation and distribution of silica throughout the material. These studies revealed increased silicon substitution with crystallisation time, overcoming favoured substitution of isolated silica in CHA and leading to the formation of silicon islands. The study was extended to analogous synthesis using dietheylamine (DEA) as an alternative SDA, identifying favourability towards isolated framework silicon substitution due to increased charge compensation. The crystallisation process of SAPO-18 (AEI) was investigated using di-isopropylethylamine (Di-PEA) with high silicon concentration to reveal increased silicon substitution and hence increased acidity with crystallisation time. A recently reported synthesis method involving a new SDA N,N-dimethyl-3,5-dimethylpiperidinium hydroxide (DMDMP) with co-template copper triethylenetetramine (CuTETA) to incorporate copper during crystallisation was investigated, confirming the control of isolated silicon substitution into the framework. The stability of these materials was investigated after high and low temperature hydrothermal aging processes. It was found that high silica SAPO-34 samples exhibit low structural integrity under high temperature hydrothermal conditions. Copper incorporation post-synthesis resulted in materials which retained superior catalytic activity after low temperature hydrothermal aging compared to materials synthesised in the presence of copper. In summary, high silica small pore materials were synthesised and evaluated for their performance for environmental control applications and identified framework silicon islands as a structural feature that enhances catalytic stability under low temperature hydrothermal conditions.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available