## 3 Results and Discussion
\begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline \multirow{2}{*}{**Entry**} & \multirow{2}{*}{**Catalyst**} & \multirow{2}{*}{\begin{tabular}{c} **Mass** \\ **cataly** \\ **(g)** \\ \end{tabular} } & \multirow{2}{*}{\begin{tabular}{c} **Conv.** \\ **(m0\%)** \\ \end{tabular} } & \multirow{2}{*}{\begin{tabular}{c} **TOF** \\ **(h\({}^{-1}\))** \\ \end{tabular} } & \multirow{2}{*}{\begin{tabular}{c} **O** \\ **OH** \\ \end{tabular} } & \multirow{2}{*}{\begin{tabular}{c} **O** \\ **OH** \\ \end{tabular} } & \multirow{2}{*}{\begin{tabular}{c} **O** \\ **OH** \\ \end{tabular} } & \multirow{2}{*}{\begin{tabular}{c} **O** \\ **OH** \\ \end{tabular} } & \multirow{2}{*}{\
\begin{tabular}{c} **O** \\ **OH** \\ \end{tabular} } & \multirow{2}{*}{
\begin{tabular}{c} **O** \\ **OH** \\ \end{tabular} } \\ \hline
1 & Blank & - & \(<\)5 & - & - & - & - & - \\
2 & Al-SBA-15 & 0.1 & \(<\)5 & - & - & - & - & - \\
3 & Zr-SBA-15 & 0.1 & \(<\)5 & - & - & - & - & - \\
4 & FeZrCF & 0.05 & 30 & 125 & 22 & 78 & - & - \\
5 & FeAlCF & 0.05 & 20 & 52 & 36 & 64 & - & - \\
6 & PdAlCF & 0.05 & \(<\)10 & - & - & 96 & - & 4 \\
7 & PdAlSBA-BM & 0.05 & \(<\)10 & - & - & 94 & - & 6 \\
8 & 5\%Pd/C & 0.05 & 22 & 19 & - & 66 & 27 & 7 \\
9 & 5\%Pd/C & 0.1 & 33 & 14 & - & 88 & 6 & 6 \\
10 & 5\%Pd/C & 0.1 & 36 & 14 & - & 86 & 7 & 7 \\ \hline \hline \end{tabular}  
* Reaction conditions: 0.1 mL LA, 0.3 mL FA, 30 min microwave irradiation, 200 \({}^{\circ}\)C, 300 W (maximum power output); b Reaction run at 150 \({}^{\circ}\)C.  
\end{table} 
Table 2: Liquid-phase microwave-assisted hydrogenation of LA using different catalysts a.  
Figure 2: TEM micrographs of FeAlCF (**left**) and FeZrCF (**right**). relatively good activity of the systems per active site as compared to noble metal-based literature reported catalysts [17,19,22,31,32]. GVL selectivity significantly varied from FeAl to FeZr systems (60%-75%), with a maximum of 75%-80%. The combined analysis of GC-MS and NMR also confirmed that significant amounts of interesting C\({}_{5}\) products (e.g., pentenoic acid) were also formed together with major product GVL obtained in the reaction. This was particularly interesting and unexpected in the case of FeAlSBA (Table 2, Scheme 1) for which selectivities of _ca_. 35%-40% to pentenoic acid were observed under the investigated reaction conditions. Comparatively, similarly-prepared flow PdAlCF catalyst and the analogous mechanochemically-prepared Pd nanocatalyst exhibited an almost negligible conversion in the system. These results confirmed that the potential of the proposed Fe-based systems over noble metals under the investigated conditions. Furthermore, the use of a commercial 5% Pd/C catalyst (_ca._ 10 times higher metal loading) provided only a slightly improved conversion of LA pushing reaction conditions but remarkably reduced TOF values (Table 2). Under comparable conditions (Table 2, entries 4 _vs._ 8) product yields were also inferior for 5% Pd/C as compared to FeZrCF, with also reduced GVL selectivities. Doubling the amount of catalyst, both conversion and GVL selectivity increased up to comparable levels to those observed for FeZrCF, although with significantly different TOF and TON values. Importantly, the catalytic systems based on Fe were found to be stable under the investigated conditions, particularly in the presence of aqueous media and formic acid, exhibiting similar catalytic activities after three uses (only 20% reduction of the initial activity was observed under the microwave-assisted conditions). These results are in good agreement with the good stability of analogous Cu-based systems employed in the conversion of LA under microwave irradiation [30]. Comparative reactions under conventional heating provided no significant activity in the conversion of LA for any of the present catalytic systems even after 12 h of reaction.