## 4 Solketal Synthesis
### Catalyst Study  
#### 4.2.1 Recent Advances on Catalysts  
Most of the recent studies on solketal synthesis comprise the development of heterogeneous catalysts or homogeneous catalysts that can be recovered, as seen in Table 1, where the most recent studies on catalysts performance are summarized. Despite being a relatively simple reaction, the ketalization of glycerol with acetone faces the previously mentioned challenges: thermodynamic limitation and mass transfer resistance. From the catalyst development point of view, to overcome the mass transfer resistance, it is preferable to avoid microporous catalysts [69]. As for the thermodynamic limitation, by exploiting the differences in affinity with the solid phase, water separation may be promoted, and the direct reaction can be fostered. This can be accomplished by using hybrid solids with higher affinity to water than to solketal, such as ion exchange resins; therefore, the by-product is adsorbed and the direct reaction is favored [11, 70, 71]. Furthermore, the catalyst must be water tolerant to preserve the active sites along the reaction and it must remain active after more than one cycle, ideally with large production capacity [58, 72]. \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
**Author** & **Catalyst** & **Acidity** & **Reaction** & **Results (\%)** & **Reusability** & **Ref.** \\ \hline Homogeneous Catalys & & & & & & \\ \hline \multirow{2}{*}{Eposito, 2019} & Iron (III) Complex & & GA = 1:4 & \(\chi_{phy}>99\%\) & \multirow{2}{*}{N.A. 1} & [73] \\  & FeCls (1-NO\({}_{2}\)) & N.A. 1 & T = - & \(\chi_{phy}>99\%\) & & \\  & 0.05 mol\% (glycerol) & & t = 90 min & \(\mathrm{Sel}\geq 98.5\%\) & & \\ \hline \multirow{2}{*}{Da Silva, 2020} & Fe (NO\({}_{3}\))\({}_{3}\)\({}_{9}\)H\({}_{2}\)O & & GA = 1:20 & & \\  & 0.30 mol\% \({}^{2}\) & N.A. 1 & T = 298 K & \(\chi_{phy}=98\%\) & & \\  & & t = 60 min & \(\mathrm{Sel}=97\%\) & & \\ \hline Zoelites & & & & & \\ \hline \multirow{2}{*}{Marjunathan, 2015} & H-Beta & & GA = 1:2 & \(\chi_{phy}=86\%\) & \multirow{2}{*}{One cycle without significant activity} & \\  & 5 wt\% (glycerol) & 1.51 & T = 301 K & \(\mathrm{Sel}=98.5\%\) & & \\  & & t = 60 min & \(\mathrm{Sel}=98.5\%\) & & \\ \hline \multirow{2}{*}{Rossa, 2017} & H-Beta & & GA = 1:4 & \(\chi_{phy}=72.62\%\) & \multirow{2}{*}{A 22\% decrease on the activity after the first use. Activity remained until} & \\  & 5 wt\% (glycerol) & 0.094 & T = 333 K & \(\mathrm{Sel}=98.3\%\) & & \\  & & t = 60 min & \(\mathrm{Sel}=98.3\%\) & & \\ \hline \multirow{3}{*}{Kowalska-Kus, 2017} & MFI & 0.369 & GA = 1:2 & \(\chi_{phy}=85,85,80\%\) & \\  & Beta & 0.388 & T = 343 K & \(\mathrm{Sel}<99\%\) & & \\  & MOR 1 wt\% (glycerol) & 0.55 & t = - & \(\chi_{bulk}=80\%\) & & \\ \hline \multirow{2}{*}{Talebian–Kikalalaieb, 2019} & HR/\(\gamma\)-N\({}_{20}\) & & & & & \\  & 10 wt\% (glycerol) & 1.806 & Ca = 1:12 & \(\chi_{phy}=100\%\) & & \\  & 10 wt\% (glycerol) & & t = 90 min & \(\chi_{bulk}=97.9\%\) & & \\ \hline \multirow{2}{*}{Ion Exchange Resins} & & & GA = 1:12 & \(\chi_{phy}=96\%\) & & \\  & 0.5 wt\% \({}^{2}\) & 5.11 & T = 313 K & \(\chi_{phy}=96\%\) & & \\ \hline \multirow{2}{*}{Esteban, 2015} & Lewati CF101 & & & & & \\  & 0.5 wt\% \({}^{2}\) & 5.11 & T = 313 K & \(\chi_{phy}=96\%\) & & \\  & & & T = 240 min & \(\chi_{bulk}=80\%\) & & \\ \hline \multirow{2}{*}{Cornejo, 2019} & Purolite CT275 & & GA = 1:2 & \(\mathrm{T}=323\) K & \(\chi_{phy}=93\%\) & & \\  & 5 wt\% (glycerol) & 5.2 & T = 300 min & \(\mathrm{Sel}=93\%\) & & \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Summary of the recent investigations (from 2015 on) on catalysts for the synthesis of solketal. \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline