## 1 Introduction  
The use of conventional fossil fuels for energy production has led to serious global consequences for the environment and climate. Renewable fuels have gained increasing attention in recent years to combat the current climate issues. Formic acid (HCOOH) has proven immensely popular as a favourable hydrogen storage/generation material due to its high gravimetric and volumetric hydrogen capacity, ease of handling, non-toxicity, stability at room temperature, and abundant supply from the conversion of biomass and carbon dioxide (CO\({}_{2}\)) [1]. The decomposition of formic acid reaction can be conducted in a liquid phase (at temperatures lower than 373 K) as well as in a gas phase (at excess temperatures), resulting in the dehydrogenation or dehydration pathways [2]. The former produces CO\({}_{2}\) and hydrogen (H\({}_{2}\)) as products, and the latter generates carbon monoxide (CO) and water (H\({}_{2}\)O) products. Performing the reaction at high temperatures (greater than 423 K) may lead to lower selectivity in the hydrogen production, because of the reverse water-gas shift reaction. Therefore, selective catalysts for formic acid dehydrogenation under these conditions are in high demand [3]. In recent years, heterogeneous catalysts have attracted large interest for formic acid decomposition because of enhanced separability, reusability, and relatively low reaction temperatures (less than 80 \({}^{\circ}\)C). The heterogeneous catalysts Pd, Au, or Ag and their alloys have been commonly studied [4; 5; 6; 7; 8; 9; 10; 11; 12; 13; 14; 15; 16; 17; 18; 19; 20; 21]. A variety of materials have additionally been investigated as catalyst supports for the dehydrogenation of formic acid, such as activated carbon [22; 23; 24], zeolites [16; 25], amines [26; 27; 28; 29], metal organic frameworks (MOFs) [11; 13; 30; 31], and macrorecticular resins [32; 33; 34]. The Pd/C catalyst is the most common and effective catalyst for H\({}_{2}\) production from formic acid in aqueous solution [35]. [PERSON] et al. investigated the performance of a commercial 5 wt.% Pd/C catalyst for the catalytic, additive-free decomposition of formic acid at mild conditions. The catalyst displayed an excellent 99.9% H\({}_{2}\) selectivity and a high catalytic activity (TOF = 1136 h\({}^{-1}\)) at 30 \({}^{\circ}\)C toward the selective dehydrogenation of formic acid to H\({}_{2}\) and CO\({}_{2}\)[5]. Formic acid decomposition for H\({}_{2}\) production has recently been investigated using Pd/ZnO catalysts, which are typically used for methanol steam reforming. [PERSON] et al. [3] investigated the catalytic properties of PdZn/ZnO in formic acid decomposition. In addition, these catalysts were compared with Pt/ZnO and Pd/Al\({}_{2}\)O\({}_{3}\) catalysts as well as ZnO support. The results show that the measured catalyst activity corresponds to the following sequence: Pd/Al\({}_{2}\)O\({}_{3}\)\(\geq\) Pd/ZnO > Pt/ZnO > ZnO. The Pd/ZnO catalyst shows the highest selectivity to hydrogen (up to 99.3%). This is attributed to the PdZn alloy formation during the catalyst reduction pretreatment. Increasing the pretreatment temperature from 573 K to 773 K resulted in a significant increase in the mean size of the PdZn (PtZn) nanoparticles. However, the activity of the catalyst remains unchanged, though the hydrogen selectivity increases. [PERSON] et al. [35] investigated Pd-supported catalysts for enhancing the decomposition of formic acid. The porous carbon support was synthesised using zeolitic imidazole frameworks (ZIFs) as a precursor. Furthermore, the porous carbon was produced by the one-step method. By doping the Zn into the predetermined bimetallic ZnCo-ZIFs, the operation of the catalyst was enhanced. The greatest catalytic activity of the prepared catalyst (Pd/Co@CN-2), with a 2.6 nm average diameter of PdCo, was observed when the Zn/Co molar ratio was 2 and demonstrated an initial turnover frequency value (TOF) as high as 2302 h\({}^{-1}\) at 30 \({}^{\circ}\)C.  
[PERSON] et al.