Preparation and Characterization of Ru-Based Catalyst for Power to Gas Applications

Abstract

Heterogeneous catalysis plays a crucial role in various industrial processes, representing a key aspect also in the energy transition for the development of new technologies. Among them, Power to Gas (PtG), belonging to the e-fuels category, requires a deep study of catalysis to convert CO₂ and green hydrogen coming from the water electrolysis with renewable power into synthetic methane, contributing to carbon-neutral goals and net-zero emission targets. In this context, the preparation and characterization of Ru-based catalyst on alumina support are carried out through a patented experimental procedure to evaluate performance parameters for PtG applications. Two main preparations are performed to assess the differences of the final product, which is a 0.5 wt% Ru on 1/8” alumina sphere support in the dry form. In the first case, a laboratory-scale production is carried out to produce 300 g of catalyst (Batch 1), while in the second one, the preparation is brought to 3 kg of catalyst (Batch 2) by using a pilot plant. In both cases, wet impregnation technique is used to prepare the Ru-based catalyst. Beyond the production, analytical tests are performed to evaluate the main features of the product and ascertain the differences between the two productions.

1. Introduction

The global energy landscape is witnessing a significant change towards more environmentally friendly and alternative energy options to tackle climate change and decrease our dependence on finite fuels [1,2]. The move towards sustainable and renewable energy sources is increasingly crucial in light of the challenges posed by global climate change [3,4]. Among energy transition technologies, Power to Gas (PtG) is gaining attention because of its innovative characteristics [5,6,7]. It allows to convert CO₂ coming from different sources and green hydrogen produced by water electrolysis with renewable energy into synthetic fuels such as methane [8,9]. PtG allows to operate with the excess of renewable power energy to produce synthetic natural gas (SNG), which can then be stored and used as a clean energy source when needed [10,11]. This technology has the potential to address the intermittency issues associated with renewable energy sources like wind and solar power, and to provide a viable alternative to traditional fossil fuel-based energy storage solutions [12,13]. The production of SNG through PtG technology is based on the Sabatier reaction:

$$C{O}_2+4H_2\leftrightarrow C{H}_4+{2H}_{2}O \mathsf{\Delta }{H}_{R, 298 K}^0=-165{\displaystyle \frac{\mathrm{k}\mathrm{J}}{\mathrm{m}\mathrm{o}\mathrm{l}}}$$

(1)

The production of synthetic methane by using CO₂ and H₂ as reactants require an heterogenous catalyst to work with less severe operating conditions and to increase the efficiency of the process for industrial applications [14]. Although the Sabatier reaction is thermodynamically favored, the direct formation of methane from carbon dioxide and hydrogen occurs with significant kinetic limitations [15,16]. Overall, the choice of catalyst type can significantly impact the efficiency and effectiveness of the Sabatier reaction, highlighting the importance of selecting the appropriate catalyst for specific applications [17,18]. In general, heterogeneous catalysts are used in this process to facilitate the separation of the catalyst from the gaseous reaction mixture, enabling its reusability and making it a cost-effective option for industrial processes [19]. The effectiveness of heterogeneous catalysis lies in the ability of the catalyst to provide an active surface for the interaction of reactant molecules, leading to an increase in reaction rates and selectivity [20]. The selection of the catalyst is generally made considering the ability to provide a surface that interacts with the reactant molecules, facilitating the formation of temporary bonds and lowering the activation energy of the reaction [21]. In fact, through the adsorption process, temporary binding of reactant molecules to the catalyst surface enables the breaking and formation of chemical bonds to occur more readily. Understanding the mechanisms of catalysis and the properties of different catalysts is essential in selecting the most suitable catalyst for a given reaction, optimizing conditions, and maximizing the desired outcomes [22,23]. In industrial applications, by enabling more sustainable and efficient processes, the right choice of the catalyst can contribute to reduce energy consumption, waste generation, and environmental impact, making it an essential tool in advancing the principles of green chemistry [24,25]. Various metals, such as cobalt and nickel on different supports, are examined in literature [26]. Among them, Ni-based catalyst is deeply investigated because of its low cost and wide availability [27]. However, the interaction between the Ni particles and adsorbed CO forms volatile nickel carbonyls, which lead to the sintering of the metal particles [28,29]. Moreover, since high activation temperatures are needed to achieve the maximum CO₂ conversion, the stability and lifetime of the catalyst is affected negatively [30]. The process can also be affected by the undesired co-production of CO through the Reverse Water Gas Shift (RWGS) reaction that occurs in a relevant way on Ni catalysts [31]. Compared to the Ni-based catalyst, noble metals such as ruthenium, rhodium, platinum, iridium, and palladium exhibit better activity in the Sabatier reaction [32]. Different literature studies underline the superior activity of Ru-based catalyst on metal oxide supports such as Al₂O₃, SiO₂, TiO₂, CeO₂, MgO, and ZrO₂ [33,34,35]. In general, the efficiency and effectiveness of a catalyst largely depend on its preparation method [36,37]. Among the most widely used techniques, wet impregnation is commonly applied for the production of heterogeneous catalysts [38]. It is a traditional method that involves the mixing of a solid support material with a solution containing the metal precursor [39]. The absorption of the solution typically occurs through capillary action, allowing for the deposition of the metal precursor onto the support surface. During the preparation, physisorption and chemisorption phenomena may occur in accordance with the operating conditions that are applied. The former allows to make weak bonds between the active phase and the support, while the latter creates strong bonds that remain permanent and mainly affect the behavior of the catalyst. Generally, depending on the type of catalyst, drying and calcination steps are also needed for the preparation [40]. One of the main advantages of wet impregnation is its simplicity and versatility. It is a relatively straightforward process that can be easily scaled up for industrial production. Additionally, wet impregnation allows for precise control over the metal loading on the support material, leading to high catalyst activity and selectivity. Furthermore, wet impregnation can be used with a wide range of metal precursors and support materials, making it applicable to a variety of catalytic systems. Several literature studies analyzed the Ru-based catalyst over alumina support for the CO₂ methanation. Garbarino et al. [41] studied a 3% Ru/Al₂O₃ catalyst to convert CO₂ into methane at atmospheric pressure. Kwak et al. [42] examined catalyst performance of a series of Ru/Al₂O₃ catalysts with Ru content in the 0.1–5% range for the reduction of CO₂ with H₂. Cimino et al. [43] evaluated the impact of alkali promoters (Li, Na, K) on the performance of the 1% Ru/Al₂O₃ catalyst for CO₂ capture and hydrogenation to methane. Porta et al. [44] studied the intraporous diffusional limitations over the Ru-based catalyst, stating that 0.5% Ru/γ-Al₂O₃ catalysts are appropriate for industrial CO₂ methanation. Falbo et al. [45] showed that the 0.5% Ru/γ-Al₂O₃ catalyst is appropriate to perform the Sabatier reaction for Power-to-Gas application. Basing on the previous considerations, this study deals with the production and analysis of a Ru-based catalyst to be used for the conversion of CO₂ and H₂ to synthetize CH₄. By following a patented experimental procedure to produce the catalyst, two different scale approaches are used: a laboratory (Batch 1) and a pilot plant (Batch 2) scale production. Various considerations are discussed about the differences of the two cases. In general, a wet impregnation method is used for both the productions. Ru-based catalyst is considered due to its high activity and selectivity under reaction condition. This catalyst allows to effectively drive the conversion of carbon dioxide and hydrogen into methane, minimizing the formation of byproducts. To enhance the dispersion and stability of active metal catalyst, an alumina support is used. By using this method, Ru precursor solutions are impregnated onto porous support materials to form active catalysts, controlling the deposition of Ru on the support surface, leading to the formation of highly dispersed and stable catalysts. All the tests are made to verify the characteristics of the product in the context of PtG applications, considering related issues that may derive from the production of synthetic methane through CO₂ methanation in a Plug Flow Reactor (PFR) in gas phase. In fact, the aim of this study consists of the preparation and characterization of a Ru-based catalyst to be used in the Power to Gas plant, evaluating the differences of the product during the scale-up from the laboratory scale to the pilot plant scale. Figure 1 shows a scheme of the Sabatier reaction over the Ru-based catalyst.

2. Catalyst Preparation on the Laboratory and Pilot Plant Scale

The Ru-based catalyst is prepared through a patented experimental procedure which is under industrial property rights protection. The preparation consists in the wet impregnation of alumina support with a precious metal solution of ruthenium. The preparation is analyzed according to two different scale processes: laboratory scale (Batch 1) and pilot scale (Batch 2). In both the cases, the support consists in an alumina sphere of 1/8” diameter, which is impregnated with a Ru solution to obtain a 0.5% Ru catalyst. The amount of catalyst that is prepared in the Batch 1 is equal to 300 g, while 3 kg of catalyst are prepared in Batch 2. Basing on these different scale, patented procedure is used for the preparation. Thus, a general preparation description is reported for both the Batch 1 and Batch 2 preparations. Figure 2 shows the block scheme of the preparation steps that is used in both the cases.

In general, the production process begins with the use of an alumina support and a ruthenium (Ru) solution. The alumina support serves as the base material, providing a stable structure for the catalyst, while the Ru solution is a key precursor that is impregnated onto the support. Since the production is carried out on a dry basis, the moisture content of alumina support is considered during the preparation. Consequently, the exact amount of alumina is weighted according to the starting moisture content, which can vary depending on the characteristics of the considered batch. This step is conducted through a thermobalance, where the moisture content is calculated subtracting the wet and dry weight of the material before and after a heating cycle, respectively. Instead, since a prepared Ru solution coming from previous processes is used for the production, the content of metal is evaluated by chemical analysis. Basing on the set ratio between Ru metal and alumina support, calculations are made to obtain the exact quantity of solution for the production. After the preliminary weighing step, the alumina support sample is subjected to a washing step to remove fine particles, since they have a high surface area which may retain a huge amount of metal during the deposition. The washing flow rate is monitored to control the correct behavior of this operation. The Ru solution is influenced by significant changes in both its physical and chemical properties, which may impact the overall production process. As the Ru solution is a key component in the preparation, this step is crucial for ensuring the proper achievement of the desired results. Specific materials and equipment are employed to guarantee optimal outcomes, along with adjustments to operational parameters that may influence the final result. Once the Ru solution has been prepared, it is then combined with the alumina support to proceed with the next stage of the process. By changing operating conditions, adsorption phenomena of Ru on alumina support such as physisorption and chemisorption are favored. In general, physisorption is a weaker physical interaction between the adsorbate and surface of the support, which is driven by intermolecular forces such as Van der Waals forces and electrostatic interactions. Contrary to physisorption, chemisorption involves the formation of strong chemical bonds, leading to a stable and irreversible interaction. After a fixed time, once the impregnation is completed, the support is subjected to a washing step to remove ions that may affect the correct use of the catalyst. In fact, they can induce the formation of acid species in a water environment, creating different problems such as corrosion of the equipment and the poisoning of the catalyst itself. Consequently, the washing step is considered a critical phase in the production process, as its characteristics have a direct impact on the final catalyst and its essential properties. The effectiveness of this step is crucial for ensuring the thorough removal of any unwanted ions from the catalyst. Any inconsistencies during this process could lead to a catalyst with suboptimal properties, ultimately affecting its overall performance in catalytic applications. Generally, hot demineralized water is used to carry away ions from the Ru-based catalyst. The ions’ disappearance is verified through conductimetry measurements and turbidity observations of the washing water. Once the wet catalyst is prepared and ions are removed, a drying step is used to obtain a Ru-based catalyst with a low content of moisture to be used as dry material. In fact, within the context of power-to-gas (PtG) technology as the intended final application, it is essential for the catalyst to be in a dry form to ensure optimal performance during the catalytic process. The presence of moisture or residual solvents can interfere with the catalyst’s activity by altering its surface properties, potentially leading to a decrease in catalytic efficiency and selectivity. Additionally, moisture may cause unwanted reactions or even degradation of the active sites, thereby reducing the overall stability and longevity of the catalyst. For these reasons, achieving a completely dry catalyst is crucial, as it guarantees that the catalyst can function at its full potential, ensuring the desired outcomes in PtG applications.

3. Characterization of the Catalyst

The characterization of the catalyst consists of different tests that allow to describe the main feature and control the quality of the prepared samples. These tests are carried out according to the Power to Gas application for the methanation process and reaction tests in Plug Flow Reactor (PFR). For both the considered cases, the tests that are performed for the characterization of the Ru-based catalyst are reported as follows: Inductively Coupled Plasma Optical Emission Spectroscopy (ICP-OES), chloride analysis, free bulk density and tapped bulk density, attrition loss, crushing test, Precious Metal Penetration (PMP), chemisorption for Metal Surface Area (MSA) determination, physisorption for Total Surface Area (TSA) determination, X-ray Fluorescence (XRF) analysis, and C and S analysis.

3.1. ICP-OES

The Inductively Coupled Plasma Optical Emission Spectroscopy (ICP-OES) instrument is a powerful analytical tool for the characterization of samples in various fields, including material science. This technology utilizes an inductively coupled plasma source to atomize and ionize samples, followed by optical emission spectroscopy to detect and quantify the elemental composition of the sample. The wide dynamic range of ICP-OES enables the simultaneous analysis of multiple elements in a single measurement, making it a time-efficient and cost-effective analytical method. To perform the analysis, an Optima 7300 DV (PerkinElmer, Waltham, MA, USA) ICP-OES spectrometer is used [46]. The instrument design and low maintenance requirements ensure reliable and reproducible results over long periods of operation. Additionally, advancements in software and automation have streamlined the data processing and reporting process, enhancing the user-friendliness of ICP-OES users. In the characterization procedure, ICP-OES is used to determine the content of ruthenium in the catalyst and verify the correct preparation of the sample. For this analysis different reactants are used, such as deionized water, Na₂O₃, HCl, HBF₄, and standard solutions for the ICP-OES instrument. The analysis requires grinding and drying steps of the Ru-based catalyst to obtain a powder, which is then dissolved to create a solution. To calculate the amount of the precious metal, the percentage of precious metal is obtained through the following equation:

$$Ru [\%]={\displaystyle \frac{ICP\ast V}{W\ast {10}^6}}\ast 100$$

(2)

where ICP is the Inductively Coupled Plasma (mg/L), V is the volume of the sample (L), and W is the weight of the sample (g). The block scheme of the ICP-OES is reported in Figure 3.

3.2. Chloride Analysis

To observe the amount of chloride ions in the prepared Ru-based catalyst, two different analyses are carried out: chromatography and titration. Chromatographic analysis is a fundamental technique utilized to separate and identify components within complex mixtures. This versatile analytical method relies on the differential interaction of sample components with a stationary phase and a mobile phase, leading to the separation of individual compounds based on their distinct physicochemical properties. The resulting chromatogram provides valuable information about the composition, purity, and concentration of analytes in the sample, enabling qualitative and quantitative analysis. Regarding the aim of this study, this technology is generally used for solutions with a high presumed chloride concentration. In this study, the Ru-based catalyst is put in contact with demineralized water for a certain period in fixed operating conditions, allowing the chloride ions to transfer into the liquid phase. This latter is then analyzed with the chromatography instrument. The other method that is used for chloride analysis is titration, which is a classic analytical technique that is widely used in laboratory settings for the characterization of samples based on their chemical composition. This method involves the precise addition of a titrant to a sample solution until a chemical reaction reaches completion, leading to a quantifiable change in the concentration of a target analyte, according to the ASTM standard [47]. In this study, the Ru-based catalyst is put in contact with demineralized water to specific operating conditions and the liquid phase is analyzed, analogously to the previous case. To perform the analytic test, an OMNIS (Metrohm, Herisau, Switzerland) titrator instrument is used [48], which is a high-end automatic potentiometric titrator that consolidates all titration applications onto a single platform for efficient and safe analyses. Different compounds are used for the test, such as NaCl, HCl, and AgNO₃.

3.3. Free and Tapped Bulk Density

Since the Ru-based catalyst is prepared with the purpose of being used in a Plug Flow Reactor for Power to Gas technology and methanation applications, two different bulk density analyses are performed: free bulk density and tapped bulk density. Free bulk density is defined as the mass of a unit volume of a material in its natural or unconfined state, whereas tapped bulk density refers to the mass of a unit volume of a material after it has been tapped or compacted to remove air voids. These tests are crucial for determining the flowability, compressibility, and packing efficiency of powders and granular materials. The results obtained from these tests can help to optimize processes such as CO₂ methanation that occurs in PFR equipment in the context of PtG technology. To perform the vibration test, a SVM II (ERWEKA, Langen, Germany) tapped density tester is used [49]. Figure 4 represents a simplified scheme of the vibration test for the determination of free bulk density and tapped bulk density.

3.4. Attrition Loss

Attrition loss refers to the gradual wearing down or reduction in size of particles or materials due to friction, impact, or other forms of mechanical stress during handling or processing. Analyzing attrition loss is crucial for applications where maintaining particle size and integrity is critical for product quality and efficiency. In particular, this analysis is studied to prevent particle breakage during the PtG application in PFR equipment. By understanding and quantifying attrition loss, several variables can be optimized such as equipment design, process parameters, and material selection to minimize product degradation and improve overall operational performance. In this study, a rotary instrument is used with a sieve to collect the powder that is formed during the movement. The operation is conducted with a 20-mesh sieve to separate the lost powder from the catalyst, according to the operating procedures. To perform the test, a ROTAB-AS (Materials Technologies, Novara IT) rotating cylinder abrasimeter is used [50]. Figure 5 shows a simplified schematic process of the attrition loss test.

3.5. Crushing Test

Crushing tests are used as a method to evaluate the hardness of the catalyst, which can significantly impact performance, durability, and life span in industrial applications. By conducting these tests, it is possible to gain valuable insights into the mechanical properties of catalyst materials, including their compressive strength, abrasion resistance, and toughness. This information is crucial for selecting suitable catalysts for specific processes, optimizing reactor design, and predicting performance under industrial operating conditions. Moreover, crushing tests can help identify potential issues such as catalyst attrition, particle size distribution, and catalyst deactivation, allowing for informed decision-making and process improvements. For this study, 100 catalyst spheres are tested individually using the MT50 (SOTAX, Aesh, Switzerland) hardness tester [51].

3.6. Precius Metal Penetration (PMP) Analysis

The Precious Metal Penetration (PMP) analysis allows to obtain detailed images regarding the diffusion of metal into the catalyst. During the test, four catalyst spheres are cut in half to observe the metal layer that diffused form the surface toward the center, and consequently, four halves sphere are examined. For each one, four points are observed along the edge (north, south, east, and west) to obtain results from different samples and points. To perform the analysis, a Leica DM (Leica Microsystems, Milano, Italy) microscope is used [52]. Figure 6 shows a simplified scheme of the procedure that is followed for the PMP analysis.

3.7. Chemisorption Test and Metal Surface Area (MSA)

Chemisorption test is conducted to analyze the metal surface area (MSA) of the catalyst through an automated flow chemisorption analyzer called ChemBET Pulsar (Anton Paar, Boynton Beach, FL, USA) [53], which is an optimized apparatus used for compact characterization and benchtop operation. Equipped with customizable analysis sequences and an automated loop injector, gas switching, and furnace temperature control, it simplifies pulse titration and temperature-programmed analyses. The sample cell is characterized by a quartz U-tube for high-temperature chemisorption, while the primary detector consists in an oxidation and ammonia resistance (W/Re) 2-filament TCD. A stream of He is used to remove air from the sample, guaranteeing the correct functioning of the instrument, and a H₂ flushing is operated to reduce the metallic sites through a pre-treatment, for 30 min. After that, the instrument loop is loaded with CO, which is injected over the catalyst during the running in a specified amount. By measuring the quantity of CO that is present before and after the operation, it is possible to calculate the amount of CO that is chemisorbed to Ru active sites on the catalyst surface. The calculations of this analysis are carried out considering the atomic area of CO. The criterion set to finish the chemisorption consists of obtaining at least three saturated peaks, which means that all the Ru active sites are occupied from CO.

Table 1. Parameters of the chemisorption test for both the Batch 1 and Batch 2 cases.

Percent of Sample Mass [%]	Atomic Weight	Stoichiometry Factor	Atomic Cross-Sectional Area [nm2]	Density [g/cm3]
0.50	101.07	1.0	0.1620	12.30

reports the main input information of the instrument for both the cases.

3.8. Physisorption Test and Total Surface Area (TSA)

Physisorption test is carried out to examine the total surface area (TSA) of the catalyst through an automated surface area and a porosity analyzer called TriStar II Plus (Micrometrics Instrument Corporation, Norcross, GA, USA) [54], which provides a comprehensive insight for production and quality control. In order to determine the surface area, catalyst samples undergo a pre-treatment process involving the application of a combination of heat, vacuum, and gas flow to eliminate contaminants absorbed from exposure to the atmosphere. Subsequently, the samples are subjected to vacuum conditions at low temperatures to cryogenic levels. Following this step, N₂ is introduced into the cell in controlled increments. Upon each gas dosing, the pressure is allowed to reach equilibrium, after which the quantity of gas absorbed by the samples is measured. The gas adsorbed at each pressure level, under constant temperature, serves to generate an isotherm from which the quantity required to establish a monolayer of gas molecules on the surface and pores of the samples can be calculated. The surface area determination involves the conditions for creating a monolayer of gas molecules on the sample. By extending this process to allow the gas to condense inside the pores, it is possible to evaluate the pore structure. To perform the analysis, BET (Brunauer–Emmett–Teller) and BJH (Barrett–Joyner–Halenda) methods are considered during the test. The parameters used for the physisorption operation, such as sample information, tube information, and operating conditions, are reported in

Table 2. Parameters of the physisorption test for both the Batch 1 and Batch 2 cases.

Type	Description	Value	Unit of Measure
Sample information	Empty tube	32.56	g
	Sample + tube	33.37	g
	Sample mass	0.80	g
	Density	0.43	g/cm3
Tube information	Sample tube	0.5	inch
	Ambient free space	1.00	cm3
	Analysis free space	1.00	cm3
	Non-ideality factor	6.2 × 10−5	-
Operating conditions	Evacuation rate	0.67	kPa
	Vacuum level	1.33 × 10−4	kPa
	Evacuation time	10	min
	Batch temperature	−195.85	°C
	Temperature ramp rate	10	°C/min
	Target temperature	30	°C
	Hold pressure	13.3	kPa
	Equilibrium interval	30	s

.

3.9. XRF

An XRF (X-ray Fluorescence) analysis is conducted to determine the composition of elements in the catalyst sample, by using a semiquantitative approach with an XRF spectrometry, called Zetium (Malvern Panalytical, Worcestershire, UK) [55]. Before the XRF analysis, the catalyst must be treated to obtain a pellet. In particular, the catalyst sample is subjected to a grinding step in order to create a powder, which is subsequently compressed into a pressing machine that operates with a ramp program reaching 300 N. The XRF analysis consists of the interaction of X-rays with a material to determine its element composition. When X-rays are directed towards a material, a portion of the X-rays penetrate the material, while others are assimilated by it. The absorbed X-rays undergo interactions at the atomic level within the material, leading to effects such as emission of photons, electrons, and fluorescent X-rays. Thus, for a single element it is possible to obtain different XRF peaks, which are typically present in the spectrum with varying intensities.

3.10. Carbon and Sulphur Analysis

To determine the possible presence of carbon and sulfur due to contaminations, the C and S analysis is carried out through the LECO SC-144DR instrument (LECO Corporation, St. Joseph, MI, USA) [56], which consists mainly of a high-efficiency furnace and infrared (IR) cell. During the analysis process, a sample is weighed into a combustion boat before being placed into a furnace set at a precise temperature of 1350 °C, creating a pure oxygen environment. As the sample combusts, carbon is released in the form of CO₂ gas, while sulfur forms are oxidized and released as SO₂ gas. As the combustion gases exit the furnace, they pass through anhydrone tubes to remove moisture before reaching the flow controller, which regulates the flow of the gases through the NDIR (non-dispersive infrared) sulfur and carbon detection cells. These cells work on the principle that CO₂ and SO₂ absorb infrared energy at specific wavelengths within the infrared spectrum. Two catalyst powder samples for each case are prepared (a, b for Batch 1 and c, d for Batch 2) to evaluate the concentration of C and S, taking into account possible measurements errors. The main input characteristics of the instrument are reported in

Table 3. Parameters of the SC-144DR Sulfur/Carbon instrument.

Parameter	Value	Unit of Measure
Low Sulfur IR Cell	8.72	V
High Sulfur IR Cell	8.56	V
Carbon IR Cell	8.45	V
Oven Temperature	48.62	°C
Furnace Temperature	1322	°C
Current limit	12	A

.

4. Results and Discussion

The results of the tests performed in this work are reported in this section, according to the analysis and methodology description discussed previously. In particular, the attention is mainly focused on the characterization results of the Ru-based catalyst that is produced. The tests are conducted in triplicate to address variability and enhance the accuracy of the measurements. All the results are discussed in the context of PtG applications for PFR reactor operating in gas phase. The results of the following analysis are discussed: Inductively Coupled Plasma Optical Emission Spectroscopy (ICP-OES), chloride analysis, free bulk density and tapped bulk density, attrition loss, crushing test, Precious Metal Penetration (PMP), chemisorption for Metal Surface Area (MSA) determination, physisorption for Total Surface Area (TSA) determination, X-ray Fluorescence (XRF) analysis, and C and S analysis.

4.1. Preparation Results

In this section, the results of both the Batch 1 and Batch 2 production are discussed in accordance with the produced catalyst. As example, different images of the Batch 2 production are illustrated to underline some feature of the catalyst and carry out some consideration about various parameters. The moisture of the alumina is measured to characterize the support and consequently weigh the correct amount of material on a dry basis.

Table 4. Results of the moisture content in the alumina support.

Type of Production	Moisture Content (%)	Specific on Dry Catalyst (g)	Amount of Alumina Support That Is Weighted (g)
Batch 1	0.59 ± 0.02	300.00 ± 0.01	301.77 ± 0.01
Batch 2	0.64 ± 0.02	3000.00 ± 0.01	3019.20 ± 0.01

reports the moisture content of alumina support for both the Batch 1 and Batch 2 production.

In both cases, the amount of Ru that is recorded in the metal solution is equal to 18.48 ± 0.01 wt%. From this data, the consequent amount of solution is weighted to obtain the right ratio between Ru metal and alumina support in the two different cases. Figure 7 shows an example of the preparation steps for the pilot plant scale production (Batch 2). Ru solution and alumina support 1/8” spheres that are used in the impregnation step (Figure 7a,b). The Ru solution presents a dark red color which tends to black because of the high concentration of the dispersed metal, while alumina support spheres appear of a white color. After the impregnation step, which allows to deposit the Ru metal on the alumina support, different colors are obtained (Figure 7c). From the results it is possible to distinguish different families of catalyst basing on different colors. These results depend on the porosity of the alumina support. After the washing steps that allow to remove chloride ions, the catalyst is present in wet conditions as shown in Figure 7d,e. In both the Batch 1 and Batch 2 production, the content of moisture that is registered after the drying step on the final product is <2%. The aspect of the Ru-based catalyst at the end of the preparation is reported in Figure 7f.

It is essential to emphasize that the active phase of Ru supported on alumina is in its metallic form. In fact, metallic ruthenium is among the most effective catalysts for the Sabatier process in the Power-to-Gas process due to its unique catalytic properties. In its metallic state, ruthenium demonstrates high activity for CO₂ hydrogenation, efficiently dissociating molecular hydrogen and facilitating the activation and reduction of CO₂.

4.2. ICP-OES Results

The ICP-OES analysis allows to verify the content of Ru that is deposited on the alumina support. In both the cases, the percentage of Ru which is contained in the catalyst equals to 0.48 wt% Ru, which is very close to the value of 0.5 wt% Ru that represent the process specification. This result provides strong evidence of the production’s accuracy and indicates a high level of precision in the control of manufacturing parameters. Such stringent oversight and meticulous attention to detail in the production process ensures consistent and reliable outcomes, reflecting the robustness of the overall manufacturing approach.

Table 5. Results of the ICP-OES analysis for the Ru content determination.

Production	Ru Direct Fusion (wt%)	PRD 105 °C Solid Materials and Supports
Batch 1	0.48 ± 0.01	0.44 ± 0.01
Batch 2	0.48 ± 0.01	0.65 ± 0.01

resumes the results of the tests.

These results are consistent with literature studies regarding the ruthenium (Ru) content in alumina-supported catalysts, which are obtained using inductively coupled plasma optical emission spectroscopy (ICP-OES) technology, validating the accuracy and reliability of the experimental methods [57,58,59]. These properties are consistent with the standard data typically observed for catalysts used in Power-to-Gas (PtG) applications [45]. This alignment strongly suggests that the production process is executed correctly, resulting in the desired material characteristics. Furthermore, it underscores that the catalyst possesses the appropriate properties required to meet the functional and performance demands of PtG systems.

4.3. Chloride Analysis Results

The results of the chloride analysis are examined in this section. In the chromatography test the content of chloride ions that is obtained for the Batch 1 and Batch 2 production cases corresponds to 67.2 ± 0.4 mg/kg and 81.3 ± 0.4 mg/kg, respectively. Besides, the chloride content that is obtained from the titration test is equal to 61.4 ± 0.3 mg/kg and 75.1 ± 0.3 mg/kg, respectively. They represent a very low concentration according to the production characteristics (

Table 6. Results of the chromatography and titration tests for the chloride determination.

Type of Production	Chloride Content
	Chromatography Test (mg/kg)	Titration Test (mg/kg)
Batch 1	67.2 ± 0.4	61.4 ± 0.3
Batch 2	81.3 ± 0.4	75.1 ± 0.3

).

Through the comparison between the results of the two methodologies that are used to analyze the chloride content in the Ru-based catalyst, it is possible to have a confirmation about the very low concentration of the Cl⁻ ions. Consequently, the produced catalyst can be used in reactive environments where water is present, such as PtG applications, avoiding problems related to HCl formation that may affect negatively the operativity of the process. The result of the chloride analysis performed through the chromatography and titration are reported in Figure 8 the Batch 1 and Batch 2 production, respectively.

By analyzing the results, from the chromatography it is possible to observe the trends of anions as a function of time and examine the peak in the correspondence of chloride concentration. In particular, for Batch 1 and Batch 2 production anions value peaks are obtained at 5.53 and 5.48 min, respectively. Regarding the titration method, the potential and the ERC (Equivalence point Recognition Criterion) trend can be observed as a function of titrant volume. At the maximum of ERC curve, the potential value is read in the corresponding curve. The results reflect the typical values of chloride content in Ru-based alumina-supported catalyst reported in literature studies [60,61], highlighting the consistency of the findings with established research and underscoring the robustness and reliability of the analytical methods used.

4.4. Free and Tapped Bulk Density Results

The free bulk density and tapped bulk density results show similar behavior in both the Batch 1 and Batch 2 production.

Table 7. Results of free bulk density and tapped bulk density.

Production	Free Bulk Density			Tapped Bulk Density
	Weight (g)	Volume (mL)	Free Bulk Density (g/mL)	Weight (g)	Volume (mL)	Tapped Bulk Density (g/mL)
Batch 1	73.19 ± 0.01	100.0 ± 0.1	(7.319 ± 0.008) × 10−1	73.19 ± 0.01	97.0 ± 0.1	(7.545 ± 0.008) × 10−1
Batch 2	73.31 ± 0.01	100.0 ± 0.1	(7.331 ± 0.008) × 10−1	73.34 ± 0.01	95.0 ± 0.1	(7.719 ± 0.008) × 10−1

reports the results of the different tests such as weight, volume, and density. These results show how much catalyst can be tapped in PFR applications.

These results align closely with the ranges of free and bulk density documented in literature studies [62,63], thereby affirming the reliability and adherence of the experimental measurements to established research standards. This indicates that favorable outcomes can be achieved in PFR equipment for PtG applications, enhancing gas flow and ensuring efficient catalyst contact, thereby improving the overall performance of the system. These optimal bulk densities can contribute to a well-balanced reactor design, facilitating efficient heat transfer, reduced pressure drop, and increased reaction efficiency.

4.5. Attrition Loss Results

The result obtained through the attrition loss test allow to verify the mechanical resistance of the catalyst. For the Batch 1 production, starting from 100.02 ± 0.01 g of catalyst, the weight of the catalyst after the test is equal to 99.93 ± 0.01 g. The remaining part of the catalyst that is not present during the last weighing corresponds to the amount of catalyst that is loss as powder. In terms of weight percentage, the amount of catalyst that is loss equals to (8.998 ± 1.41) × 10⁻²% w/w. Instead, for the Batch 2 production catalyst, starting from 100.03 ± 0.01 g of catalyst, the final weight is equal to 99.89 ± 0.01 g, corresponding to a percentage loss of (1.399 ± 0.141) × 10⁻¹% w/w. These results show a very low loss during operations for both the cases, and this can be considered a valuable result for industrial applications.

Table 8. Results of the attrition loss analysis.

Production	Starting Weight (g)	Final Weight (g)	Percentage Loss (% w/w)
Batch 1	100.02 ± 0.01	99.93 ± 0.01	(8.998 ± 1.41) × 10−2
Batch 2	100.03 ± 0.01	99.89 ± 0.01	(1.399 ± 0.141) × 10−1

resumes schematically the attrition loss results.

According to the results obtained from the analysis, the catalyst demonstrates strong mechanical resistance, indicating its suitability for plug-flow reactors used in PtG applications and suggesting its potential to withstand the typical gas velocities within the reactor, thereby mitigating abrasion phenomena during operation. Literature studies on the attrition and abrasion characteristics of alumina catalysts reinforces the credibility of experimental methodology and results obtained in this work [64,65].

4.6. Crushing Test Results

The crushing test results performed for each considered case on 100 catalyst spheres are shown in Figure 9.

By analyzing the hardness results, a wide distribution of values is obtained. This result depends on the characteristics of the samples and can be affected from the diffusion of Ru metal into the alumina sphere support, porosity, irregular shape and size, impurities, and defects. Through statistical analysis, various parameters are evaluated based on the experimental results of both Batch 1 and Batch 2.

Table 9. Results of the crushing test for the hardness determination.

Parameter	Hardness [N]
	Batch 1	Batch 2
Max	83	80
Min	25	27
Max–Min	58	53
Mean	59.08	54.85
Harmonic mean	55.25	50.50
Median	62	56
Mode	65	51
Mean deviation	10.47	11.99
Standard deviation	13.06	14.59
Variance	170.61	212.81
Kurtosis	0.0966	−0.8117

resumes the hardness results obtained from the crushing test.

The statistical analysis of the hardness of two batches of material provides important insights for applications such as power-to-gas (PtG) processes where mechanical resistance plays a critical role. While Batch 1 exhibits slightly higher values for maximum hardness (83 N) and mean hardness (59.08 N) compared to Batch 2 (80 N and 54.85 N, respectively), the overall results are similar, with both batches demonstrating adequate mechanical properties for potential use in packed bed reactors. The small differences in parameters, such as standard deviation and variance, indicate only minor variability in hardness between the two batches. Importantly, the ranges of hardness values for both batches overlap significantly, and the mean, median, and mode values for Batch 2 remain within acceptable limits. These results suggest that Batch 2 is unlikely to pose any significant risk in terms of mechanical degradation or abrasion under typical PtG reactor conditions. Despite slight variations, both batches exhibit comparable levels of mechanical resistance, making them equally suitable for use in PtG applications. The observed differences are minimal and do not compromise the reliability or durability of the material in packed bed reactors. The hardness results obtained from the experiments are consistent with literature studies, underscoring the reliability and integrity of the data [66,67].

4.7. PMP Results

The PMP test shows different results about the diffusion of Ru into the alumina support spheres. In particular, the catalyst surface is analyzed to distinguish the thickness of the Ru layer. Basing on the observation of different samples in several directions, Figure 10 shows an example of the samples analyzed for both the Batch 1 and Batch 2 production.

By analyzing the results, it is possible to notice that the Ru metal diffuses differently in the alumina support spheres, and depending on the sample, different results are obtained. The diversity of these results depends on the characteristics of the alumina support that is used for the preparation, such as porosity and surface area. The results of PMP analysis are summarized in

Table 10. Results of the PMP test for the Batch 1 case.

Parameter	Number of the Catalyst Sphere
	1	2	3	4
PMP NORD [mm]	147.4	163.4	156.0	71.9
PMP EST [mm]	119.3	103.5	123.4	124.3
PMP SUD [mm]	86.1	156.0	339.7	87.1
PMP OVEST [mm]	87.7	118.6	127.6	35.5
PMP average [mm]	127.9
RSD [%]	51.6

and

Table 11. Results of the PMP test for the Batch 2 case.

Parameter	Number of the Catalyst Sphere
	1	2	3	4
PMP NORD [mm]	317.6	263.8	287.2	227.7
PMP EST [mm]	308.7	272.6	267.9	256.6
PMP SUD [mm]	310.1	294.5	261.9	273.9
PMP OVEST [mm]	329.6	247.0	365.1	241.8
PMP average [mm]	282.8
RSD [%]	12.7

for the Batch 1 and Batch 2 production, respectively.

Four different parameters are evaluated for each single sample to analyze the diffusion along the entire edge. Despite the dissimilarity of the diffusion results, the PMP average value respects the standard requirements that are fixed for this test. However, by confronting the two considered batches, different values of PMP average are obtained. Particularly, for Batch 1 and Batch 2 production, PMP average values correspond to 127.9 and 282.8 mm, respectively. As example, Figure 11 and Figure 12 show representative PMP test images for Batch 1 and Batch 2 production, respectively, where it is possible to observe the diffusion of ruthenium into the alumina sphere support.

By analyzing the results, it is evident that the diffusion of Ru metal into the alumina support occurs just in the external layer of the sphere. This means that only the shell of the catalyst is active for the catalytic reaction. This result respects the expectation since the catalyst is produced to be used in gas reaction applications, where only the external part is interested since the reaction is typically affected by diffusion limitations. The results are in accordance with literature studies on Ru-based on alumina support catalyst for CO₂ methanation [44,45].

4.8. MSA Chemisorption Test Results

The results of the chemisorption tests for the determination of the metal surface area (MSA) are reported in this section. For both the cases analyzed, five peaks are registered during time as TCD (Thermal Conductivity Detector), with the corresponding temperature (Figure 13).

For each peak that is registered during the test, the following parameters are evaluated: temperature at maximum, volume adsorbed, and cumulative volume. As peak number increases, volume adsorbed tends to zero, while cumulative volume stabilizes to a constant value, indicating the saturation of the active sites on the catalyst surface (

Table 12. Results of the chemisorption test for the MSA determination.

Peak Number	Temperature at Maximum [°C]		Volume Adsorbed [mL/g STP]		Cumulative Volume [mL/g STP]
	Batch 1	Batch 2	Batch 1	Batch 2	Batch 1	Batch 2
1	25.20 ± 0.01	25.40 ± 0.01	(8.05 ± 0.02) × 10−2	(5.40 ± 0.02) × 10−2	(8.05 ± 0.02) × 10−2	(5.40 ± 0.02) × 10−2
2	25.40 ± 0.01	25.50 ± 0.01	(1.23 ± 0.02) × 10−2	(4.81 ± 0.2) × 10−3	(9.28 ± 0.02) × 10−2	(5.88 ± 0.02) × 10−2
3	25.40 ± 0.01	25.40 ± 0.01	(4.81 ± 0.2) × 10−3	(1.93 ± 0.2) × 10−3	(9.76 ± 0.02) × 10−2	(6.07 ± 0.02) × 10−2
4	25.40 ± 0.01	25.40 ± 0.01	(1.75 ± 0.2) × 10−3	0	(9.94 ± 0.02) × 10−2	(6.07 ± 0.02) × 10−2
5	25.30 ± 0.01	25.40 ± 0.01	0	0	(9.94 ± 0.02) × 10−2	(6.07 ± 0.02) × 10−2

).

The results of the chemisorption test for MSA determination indicate that Batch 1 consistently outperforms Batch 2 in terms of adsorption capacity. While both batches exhibit nearly identical temperatures at maximum adsorption, suggesting similar thermal behavior and adsorption mechanisms, Batch 1 demonstrates significantly higher values for both individual and cumulative adsorption volumes across all measurable peaks. The cumulative adsorption for Batch 1 reaches 9.94 × 10⁻² mL/g STP, compared to 6.07 × 10⁻² mL/g STP for Batch 2, highlighting its superior surface area for the adsorbed gas. However, both batches show high precision, with low standard deviations across all parameters. Other relevant parameters are obtained from the analysis, indicating the characteristics of the Ru-based catalyst as reported in

Table 13. Results of the chemisorption test for the catalyst characterization.

Parameter	Value		Unit of Measure
	Batch 1	Batch 2
Sample mass	0.772 ± 0.01	0.789 ± 0.01	g
Active Loop Volume at 25 °C	0.451 ± 0.01	0.451 ± 0.01	mL STP
Cumulative Volume	0.099 ± 0.02	0.061 ± 0.02	mL/g STP
Metal Dispersion	8.96 ± 0.03	5.48 ± 0.03	%
Metallic Surface Area (sample)	0.43 ± 0.02	0.26 ± 0.02	m2/g sample
Metallic Surface Area (metal)	86.54 ± 0.02	52.91 ± 0.02	m2/g metal
Metallic adsorption capacity	19.88 ± 0.01	12.15 ± 0.01	cc CO/g PM
Active Particle diameter	5.6 ± 0.1	9.2 ± 0.1	nm

.

The results present key parameters for the two batches, providing valuable insights. Batch 1 demonstrates superior performance across all aspects, with higher metal dispersion, metallic surface area (both on the sample and metal), metallic adsorption capacity, and smaller active particle diameter compared to Batch 2. These differences suggest that Batch 1 holds greater potential for catalytic activity and adsorption efficiency, making it more suitable for applications that require enhanced surface interactions and reactivity. However, both Batch 1 and Batch 2 exhibit strong performance and are effective for their intended applications. The results are coherent with literature studies about the chemisorption on Ru-based catalysts, demonstrating similar behaviors and patterns with experimental data [68,69].

4.9. TSA Results

The results of the chemisorption tests for the determination of the metal surface area (MSA) are reported in this section in terms of surface area, pore volume, and pore size characteristics. Specifically, the adsorption and desorption parameters are evaluated to quantify the physical properties of the catalyst.

Table 14. Results of the physisorption test for the TSA determination.

Type	Description	Value		Unit of Measure
		Batch 1	Batch 2
Surface Area	Single point surface area at P/P0 = 0.0796	49.35 ± 0.02	45.82 ± 0.02	m2/g
	BET Surface Area	51.38 ± 0.02	47.68 ± 0.02	m2/g
	BJH Adsorption cumulative surface area of pores	57.11 ± 0.02	53.13 ± 0.02	m2/g
	BJH Desorption cumulative surface area of pores	61.57 ± 0.02	57.72 ± 0.02	m2/g
Pore Volume	Single point adsorption total pore volume of pores at P/P0 = 0.9855	0.333 ± 0.02	0.301 ± 0.02	cm3/g
	Single point desorption total pore volume of pores at P/P0 = 0.3107	0.0267 ± 0.02	0.0248 ± 0.02	cm3/g
	BJH Adsorption cumulative volume of pores	0.333 ± 0.02	0.301 ± 0.02	cm3/g
	BJH Desorption cumulative volume of pores	0.334 ± 0.02	0.302 ± 0.02	cm3/g
Pore size	Adsorption average pore diameter (4V/A by BET)	259.38 ± 0.03	252.58 ± 0.03	Å
	Desorption average pore diameter (4V/A by BET)	20.82 ± 0.03	20.83 ± 0.03	Å
	BJH Adsorption average pore width (4V/A)	233.20 ± 0.03	226.51 ± 0.03	Å
	BJH Desorption average pore width (4V/A)	217.01 ± 0.03	209.21 ± 0.03	Å

reports schematically all the examined variables.

Different results are registered for both the considered cases to analyze the behavior of the main parameters, during the adsorption and desorption phases. The results for surface area, pore volume, and pore size exhibit similar outcomes between the two batches, suggesting that both products possess comparable characteristics in these key areas. This similarity indicates that, despite differences in other parameters, the two batches exhibit similar structural properties, such as the distribution of pore sizes and the overall capacity for adsorption. As a result, both batches may perform similarly in applications where these specific attributes, such as surface area and pore structure, are critical to the product’s functionality and effectiveness. As reported in Figure 14 and Figure 15, it is possible to observe similar results between the Batch 1 and Batch 2 cases, in terms of isotherm linear plot, isotherm pressure composition, BET Surface Area, BJH Adsorption and Desorption Cumulative Pore Volume, and BJH Adsorption and Desorption Pore Volume. The results are in accordance with and support the findings documented in existing literature studies [57,70,71].

4.10. XRF Results

As explained before, XRF analysis requires a pre-treatment step of the catalyst in order to create a pressed pellet to be used into the XRF instrument. Figure 16 show an image of the pressed pellets obtained from the pre-treatment step.

After the XRF analysis is performed, the composition of the sample is attained revealing the various analytes contained into the catalyst. The concentration results of the different elements obtained through the semi-quantitative XRF analysis are reported in

Table 15. Results of the XRF analysis for the determination of the catalyst composition.

Analyte	Concentration [%]
	Batch 1	Batch 2
O	44.580 ± 0.003	43.807 ± 0.003
Na	0.026 ± 0.003	0.025 ± 0.003
Al	45.295 ± 0.003	45.439 ± 0.003
Si	0.034 ± 0.003	0.039 ± 0.003
P	0.001 ± 0.003	0.001 ± 0.003
S	0.001 ± 0.003	0.002 ± 0.003
Cl	0.025 ± 0.003	0.009 ± 0.003
Ca	0.033 ± 0.003	0.029 ± 0.003
Fe	0.023 ± 0.003	0.017 ± 0.003
Zn	0.007 ± 0.003	0.009 ± 0.003
Ga	0.005 ± 0.003	0.005 ± 0.003
Ru	0.438 ± 0.003	0.433 ± 0.003

.

The XRF analysis reveals that both batches share similar elemental compositions, with the major components being oxygen (O) and aluminum (Al), which constitute the largest portions in both samples. Batch 1 has slightly higher oxygen content (44.580%) compared to Batch 2 (43.807%), while the aluminum concentration is almost identical, with Batch 1 at 45.295% and Batch 2 at 45.439%. These major values suggest that both batches have comparable overall compositions and structural characteristics, which is important for catalytic performance. Other elements, such as sodium (Na), silicon (Si), and phosphorus (P), show very similar concentrations, indicating no significant differences between the batches in these areas. While chlorine (Cl) content is higher in Batch 1 (0.025%) than in Batch 2 (0.009%), this difference is relatively minor and may not have a large impact on the catalyst’s function. Similarly, variations in sulfur (S), calcium (Ca), iron (Fe), and zinc (Zn) are small and unlikely to significantly affect catalytic behavior. Both batches also contain ruthenium (Ru) in similar concentrations, with Batch 1 at 0.438% and Batch 2 at 0.433%. Given that ruthenium is a key active metal in the catalytic process, this minor difference in concentration may impact on the catalyst’s performance. However, both batches appear to be suitable for catalytic applications based on their elemental composition. Figure 17 and Figure 18 show the results of the test for both the Batch 1 and Batch 2 cases, in terms of Rmeas as function of 2Theta angle, indicating the detection of the signal for each registered relevant peak.

By analyzing the results and the trend of the different plots, it is possible to observe the output of the XRF spectrometer, which is distinguished by a background noise due to the characteristics of the instrument and considerable peaks that allows to identify the detection of the elements. Literature studies confirm the results obtained in this work through experimental XRF analysis, providing consistency to the data collected [72,73].

4.11. C and S Results

By following the methodology used for the C and S analysis, two results for each case are obtained. Since the analysis is conducted at 1350 °C, the catalyst is subjected to deactivation, which corresponds to a shift in color from grey to white, before and after the test, respectively. Figure 19 shows an example of the most relevant sample for the Batch 1 and Batch 2 after the C and S analysis.

Table 16. Results of the C and S analysis.

Sample	Type	Weight [g]	C [%]	S [%]
Batch 1	a	0.35 ± 0.01	(2.49 ± 0.02) × 10−2	Lower limit of the instrument’s measuring range
	b	0.31 ± 0.01	(1.81 ± 0.02) × 10−2
Batch 2	c	0.34± 0.01	(1.14 ± 0.02) × 10−2
	d	0.33± 0.01	(8.78 ± 0.02) × 10−2

resumes the results of the four samples examined in the C and S analyzer, indicating weight and concentration data.

By analyzing the obtained results, very low concentrations are registered for each sample. While carbon concentration is reliably registered, sulfur concentration is lower than the limit of the instrument’s measuring range. As expected, these values are negligible in the alumina–ruthenium system [57,74].

5. Conclusions

The preparation and characterization of a Ru-based catalyst on alumina support is carried out by following a patented procedure, to evaluate different performance parameters according to Plug Flow Reactor (PFR) applications in the context of Power to Gas (PtG) technology. Two main production cases are analyzed to produce the Ru-based catalyst. Both the Batch 1 and Batch 2 productions allow to produce 0.48 ± 0.01 wt% Ru-based catalyst, which is very close to the pre-established value, proving that the procedure is consistent with experimental preparation. Consequently, the wet impregnation method that is used for the Ru-based catalyst is proven effective in both the Batch 1 and Batch 2 production. These results demonstrate that the general technique can be performed in different scale approaches without changing the results in a relevant way. Ru precursor solution that is used to impregnate the alumina spheres allows to form a high disperse active phase on the support surface with a relevant stability. In both cases, the preparation leads to different color families of catalyst due to the intrinsic characteristic of the alumina support that is used for the deposition of the metal solution. In fact, from the observation of the final product, various shades of grey can be distinguished. Once the preparation is carried out efficiently and Ru-based catalyst is obtained in different scale production, analytic tests are performed to evaluate the main characteristics of the two products. A low number of chloride ions is registered during the tests, allowing the catalyst to be used in a water environment avoiding acid formation and corrosion problems. Physical properties that are examined trough bulk density, attrition, and crushing test show an adequate behavior to operating stresses that may occur in a reactant environment. In particular, free and tapped bulk density results outline an acceptable response to packing bed problems, and the small amount of catalyst that is lost during the attrition test underlines the durability of the material over time. Moreover, appropriate hardness values are obtained from crushing test results, emphasizing the integrity of the catalyst during mechanical pressure. Catalyst behavior is also examined through chemisorption and physisorption tests, while composition is evaluated through XRF analysis and C and S tests. By observing the deposition of Ru metal on the alumina support surface, it is evident that only a thin superficial layer contains the active phase, and this is in accordance with the preparation and expected results. This is in accordance with the heterogeneous catalyst that is used to perform the Sabatier reaction for PtG application; only the superficial layer of catalyst must be active for the reaction to produce synthetic methane.