## 1 Introduction  
Hydrogen is considered as one of the most promising energy sources in the near future since it is globally accepted as a promising energy carrier for producing electricity in a fuel cell using a sustainable generation pathway, taking into consideration that the only by-product of its reaction with oxygen is water, therefore a green process [1]. Moreover, hydrogen can be one of the alternative energy sources for fuel cell vehicles and portable electronic devices [2,3]. However, one of the main limitations of hydrogen storage technologies is at this moment related to (i) the capacity hydrogen storage devices and the safety hazards regarding hydrogen storage (transportation and flammability). To overcome these challenges, a range of technological approaches has been reported. Either physical or chemical storage of hydrogen is considered as alternative solutions. In the former case, hydrogen is preferentially adsorbed into materials with high surface area and porosity, such as carbon materials [4], metal-organic frameworks [5] or zeolites [6] and in the latter case, a hydrogen-rich material could be efficiently decomposed via a catalytic chemical process. Examples of these liquid-phase carriers are alcohols [7], hydrazine [8], ammonia [9] and formic acid (HCOOH) [10]. Formic acid is an important chemical product synthesised by means of biomass process. It has been reported as a safe and convenient potential storage material of hydrogen under mild conditions due to the following properties: high volumetric hydrogen content (4.4%), liquid state at room temperature, high stability, environmental benignity and nontoxicity. The decomposition of formic acid follows two main pathways, (i) dehydrogenation (HCOOH \(\rightarrow\) CO\({}_{2}\) + H\({}_{2}\), \(\Delta\)G = \(-\)48.4 kJmol\({}^{-1}\)) and (ii) dehydration (HCOOH \(\rightarrow\) CO + H\({}_{2}\)O, \(\Delta\)G = \(-\)28.5 kJmol\({}^{-1}\)), being the dehydration pathway promoted by acidity or heating. Formic acid decomposition in the liquid phase has been studied using a range of either homogeneous or heterogeneous catalysts [11]. Homogeneous catalysts have shown promising high catalytic performance, however, issues such as separation from the reaction mixture and recycling, have not been overcome yet and therefore, to achieve scaling up for commercial applications. Heterogeneous catalysts, based on supported metal nanoparticles, such as Pd, Au or Ag and their alloys have been reported in both the past and recent years [5; 12; 13; 14; 15; 16; 17; 18; 19; 20; 21; 22; 23; 24; 25]. Several supports have been used for studying the nature and influence of support, i.e., activated carbon [22; 23; 24], TiO\({}_{2}\)[26], zeolites [25], macroreticular resin [13], amines [14] and MOFs [5; 15; 16]. One of the typical methods used widely for the synthesis and deposition of metal nanoparticles is based on colloidal methods. Immobilisation of metal colloids offers the following advantages: namely, precise control of nanoparticle size and shape, narrow particle size distribution and the ability to regulate surface active sites by the choice and nature of the stabiliser/ligand [27; 28; 29; 30; 31; 32; 33; 34; 35]. We have shown previously that by choosing the appropriate ligand, varying the concentration of the precursor, amount of the ligand, reducing agent, temperature of the colloidal reduction, nature of the ligand and reducing agent can affect the final morphology and structure of synthesised nanoparticles [36; 37; 38]. In the present work, we report that by varying specific parameters of a typical sol immobilisation method we can tune the morphology of supported Pd monometallic catalysts and therefore catalytic performance. We focus on the variation of the following parameters: amount of stabiliser, Pd loading, reducing agent concentration, choice of support (activated charcoal and TiO\({}_{2}\)) and Au-Pd atomic ratio.