# Mixed Oxides: Role of Washing and Residual Ions in Transesterification Reactions

## TL;DR

This paper studies how residual sodium ions affect the properties and performance of mixed oxides used in transesterification reactions.

## Contribution

The novelty is investigating how residual chemicals influence hydrotalcites, mixed oxides, and transesterification yields.

## Key findings

- MOs from chlorides contain stable NaCl, which reduces surface area and lowers transesterification yield.
- MOs from nitrates contain unstable NaNO3, which decomposes and forms basic species that promote transesterification.
- Residual sodium's effect depends on the material precursors used in synthesis.

## Abstract

The mixed oxides (MOs) serve as catalysts for many reactions
such
as transesterification, transformation of ethanol to butanol, catalytic
cracking, or dehydrogenation reactions. MOs are usually synthesized
from hydrotalcites, which are often prepared by the coprecipitation
method. However, some chemicals can remain after coprecipitation and
influence the properties of MOs, including subsequent applications.
The novelty lies in investigating how the residual chemicals affect
the properties of hydrotalcites, MOs, and the transesterification
reaction (conducted in both one- and two-step processes). Mg–Al
and Mg–Fe hydrotalcites were synthesized from chloride and
nitrate salts via coprecipitation with NaOH, followed by washing with
varying amounts of redistilled water, resulting in variations in the
sodium ion content (more water, less sodium ions). All materials were
characterized by many analytical methods such as X-ray diffraction,
metal determination, scanning electron microscopy, textural properties,
and basicity determination. MOs synthesized from chlorides contained
stable NaCl, which is not catalytically active, and blocked the pores,
leading to a reduced surface area and, consequently, a lower transesterification
yield. In contrast, MOs prepared from nitrates contained unstable
NaNO3, which decomposed during calcination and, upon exposure
to water, formed basic species (NaOH) that promoted transesterification.
Therefore, the effect of residual sodium varies depending on the material
precursors. This understanding helps us to improve the synthesis of
hydrotalcites and mixed oxides.