## 2 Results and Discussion  
Table 1 summarizes key catalysts properties, in terms of particle size, porosity, morphology, and acid density, along with their acronyms. The efficiency of A-15, PS-pTsOH, and Aquivion mP98 in the esterification reaction of levulinic acid (LA, **1**) has been tested first by employing 1-pentanol (**2**) as a reference alcohol substrate (Scheme 1). Taking into account the earlier discussion, the swelling behavior of the three different resins after \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline \begin{tabular}{c} **Catalyst Name** \\ \end{tabular} & \begin{tabular}{c} **Particle Size** \\ **(mm)** \\ \end{tabular} & \begin{tabular}{c} **Surface** \\ **Area (m2\({}^{3}\)/g)** \\ \end{tabular} & \begin{tabular}{c} **Pore Volume** \\ **(cm\({}^{3}\)/g)** \\ \end{tabular} & \begin{tabular}{c} **Matrix 1** \\ **(cm\({}^{3}\)/g)** \\ \end{tabular} & \begin{tabular}{c} **Swelling** \\ **Volume 2 (\%)** \\ \end{tabular} & \begin{tabular}{c} **Acid Loading 3** \\ **(mmol/g)** \\ \end{tabular} \\ \hline A-15 & \textless{}0.3 1 & 45 1 & 0.4 1 & \begin{tabular}{c} \begin{tabular}{c} Styrene/DVB \\ (macroreticular) \\ \end{tabular} & 10 & 4.7 \\ \hline PS-pTsOH & 0.25–0.59 1 & 3.26 & 0.0036 & \begin{tabular}{c} Styrene/DVB \\ (macroporous) \\ \end{tabular} & 50 & 2.9 \\ \hline Aquivion & \begin{tabular}{c} \\ mP98 \\ \end{tabular} & \
\begin{tabular}{c} -0.70 \\ \end{tabular} & - & - &
\begin{tabular}{c} Tetafluoroethylene/ \\ sulfonylfluoride vinyl \\ ether (non-porous) \\ \end{tabular} & 400 & 1.02 \\ \hline \hline \end{tabular}  
* Data provided by the manufacturer. 2 1-Pentanol, r.t. 3 Determined by elemental analysis.  
\end{table} 
Table 1: Key properties of the tested catalysts. contact with 1-pentanol has been also evaluated. In this regard, the increase in volume produced by swelling for the resins featuring very low to no-porosity in the dry state can reach values of up to 400% (Table 1 and Figure SI, Supplementary Materials, SM). The most significant data collected from the batch runs are summarized in Tables 2-4. The blank reaction experiment, in the absence of a catalyst, gave a LA conversion of \(\sim\)4% after 24 h of reaction time (Table SI, entry 1, SM), thereby indicating a negligible extent of the esterification of levulinic acid by auto-catalysis under the tested reaction conditions. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Entry** & **Catalyst (mol \%) 1** & **LA/1-Pentanol** & **T (\({}^{\circ}\)C)** & **t (h)** & **C (\%) 2** \\ \hline
1 & 4.3 & & & & 5 & 45 \\
2 & 8 & & & & 62 \\
3 & 10 & & & & 64 \\ \hline
4 & 4.3 & & & 12 & 46 \\
5 & 8 & & & & 66 \\
6 & 10 & & & & 67 \\ \hline
7 & 4.3 & & & & 24 & 53 \\
8 & 8 & & & & 70 \\
9 & 10 & & & & 72 \\ \hline
10 & 4.3 & & & & 5 & 50 \\
11 & 8 & & & & 68 \\
12 & 10 & & & & 70 \\ \hline
13 & 4.3 & & & & 12 & 53 \\
14 & 8 & & & & 69 \\
15 & 10 & & & & 73 \\ \hline
16 & 4.3 & & & & 24 & 62 \\
17 & 8 & & & & 73 \\
18 & 10 & & & & 76 (73) 3  \\ \hline
19 & 4.3 & & & & 5 & 47 \\
20 & 8 & & & & 58 \\
21 & 10 & & & & 59 \\ \hline
22 & 4.3 & & & 12 & 49 \\
23 & 8 & & & & 75 \\
24 & 10 & & & & 77 \\ \hline
25 & 4.3 & & & 24 & 60 \\
26 & 8 & & & & 82 \\
27 & 10 & & & & 86 \\ \hline
28 & 4.3 & & & & 5 & 50 \\
29 & 8 & & & & 63 \\
30 & 10 & & & & 68 \\ \hline
31 & 4.3 & & & 12 & 58 \\
32 & 8 & & & & 76 \\
33 & 10 & & & & 86 \\ \hline
34 & 4.3 & & & 24 & 66 \\
35 & 8 & & & 78 \\
36 & 10 & & & 92 (88)  \\ \hline \end{tabular}
\end{table} 
Table 2: Esterification reaction of Levulinic Acid (LA) **1** with 1-pentanol (**2**) catalyzed by Aquivion mP98. Aquivion mP98 was found to be the most efficient catalyst, selectively providing up to 92% LA conversion towards the target product **3** after 24 h at 90 \({}^{\circ}\)C (Table 2, entry 36). Moreover, the product was isolated in high yield (88%) and purity (>98%) by a simple work up procedure (see Section 3). Notably, unreacted 1-pentanol could be nearly quantitatively recovered (96%) by distillation at 75 \({}^{\circ}\)C under vacuum (80 mmHg) for later reuse.