Catalysts play a crucial role in the modern chemical industry, and indirectly the development of society. According to statistics, there are around 30,000 different raw materials and chemical intermediates that are synthesized by using catalysts. These materials are not only related to people’s food, clothing, and housing, but also involve modern high-tech fields such as information transmission, network technology, aerospace [1
], and bioengineering [4
]. Today, researchers are committed to developing more efficient, selective, less expensive, and greener industrial catalysts in order to upgrade current chemical production technologies.
Heterogeneous catalysts are the most widely used catalysts in industrial production, due to their versatile physicochemical properties, high hydrothermal stability, and efficient catalyst recovery/reusability [6
]. Indeed, heterogeneous catalysis contributes to about 90% of chemical production processes and to more than 20% of all industrial products [8
]. There are numerous types of catalytic materials and supports, among which zeolite, mesoporous catalyst, resin catalyst, alumina, and activated-carbon-based catalysts are typically used in industry. Usually, the characteristics of a catalyst, such as specific surface area, particle size, morphology, porosity, and acidity, are determined, as they are crucial parameters for performance and use in industrial applications. However, the effect of the heat capacity of catalysts on large-scale chemical processes has not received much attention in the literature, even though the thermodynamic properties vary significantly between different catalysts or catalyst supports. Industrial processes can be performed under non-isothermal conditions with different types of catalysts and catalyst loadings, and many processes are performed in continuous reactors with high catalyst loads. Determining the thermal properties of a catalyst is necessary when evaluating the thermal risk of a process performed under non-isothermal conditions, especially when considering larger-scale production. Besides risk assessment, the heat capacity of the catalyst can influence the operation and temperature profile of a reactor significantly. This issue often arises at the start of a process. The heat capacity of a large catalyst bed can have a significant impact on the energy balance. These aspects can be very important for robust modeling and simulation purposes, which are the basis of the reliable design and operation of chemical processes. However, much attention has typically been focused on determining the physical properties of the bulk phase [9
] in detail, including heat capacity, while very little data are found for heterogeneous catalysts [12
Differential scanning calorimetry (DSC) [14
] is a conventional method for measuring a variety of thermodynamic properties. It has been widely applied to the specific heat capacity (Cp
) measurement of different materials, such as frying oil [15
], alloys [16
], phase change materials [17
], and solid lead [18
]. However, the sensitivity of measuring and calculating specific heat capacity by general DSC is usually very low, resulting in a relative error of 5–10%, mainly due to the weak baseline reproducibility. In addition, poor correction accuracy is obtained by this method. The calibration of general DSC instruments is usually performed by melting the standard metal, and it is greatly affected by the sample morphology, reaction type, and atmosphere. Moreover, sample adaptability is very poor. The sample is always required to maintain good contact with the bottom of the crucible to ensure excellent heat conduction; thus, the Cp
test of powders and large heterogeneous samples is greatly restricted. Furthermore, liquid samples are also not applicable, as small crucibles (<100 μL) are usually used, which are difficult to seal.
The Setaram C80 3D Calvet Calorimeter is powerful and flexible. Measurement by C80 is similar to DSC, i.e., the energy difference between the measured substance and the reference substance is determined under a programmed-temperature control. However, the Calvet calorimeter possesses a caloric efficiency of up to 94%, whereas that of typical plate DSC is between 20 and 40%. Besides this, the detector adopts a three-dimensional full-clad calorimetric method, and, contrary to the general DSC, it takes into account the heat flow that may occur inside the sample itself during calorimetry. The C80 measurement is independent of the weight, form, and nature of the sample, the type of cell utilized, the manner of contact between sample and sensor, and the nature of the sweeping gas (inert, oxidizing, wet, etc.), providing an excellent precision, even for samples with irregular shapes or uneven heat conduction. Furthermore, the temperature is raised and lowered at a very consistent, slow rate, which makes the Cp
measurement more accurate. The C80 calorimeter has found an application in the precise determination of heat capacities of different materials [19
In this work, a micro-calorimeter (C80) was for the first time applied for determining the specific heat capacity of commonly used catalytic materials/supports as a function of temperature. These data contribute to filling an important gap in knowledge in this area. The data can be used to estimate the kinetic constants and reaction enthalpies of chemical processes at both laboratory and industrial scale. Moreover, the heat capacities are important basic data for safety and risk assessment purposes.
In this study, the evolution of specific heat capacity with temperature was measured for different materials used in the preparation of heterogeneous catalysts. Such a study is important in developing efficient and safe chemical processes.
A commercial Tian–Calvet calorimeter was successfully used, allowing for high accuracy and the possibility of working at high temperatures.
Different families of catalytic materials were tested, including alumina-silicates, aluminum oxide, silicon dioxide, titanium dioxide, activated carbon, and sulfonated resin. It was found that the specific heat capacities increase, to a varying degree, with temperature for these catalytic materials. For example, the Cp of silicon dioxide was more sensitive to a temperature increase than titanium dioxide.
A polynomial correlation for each catalytic material was developed. However, there is not a clear correlation between the Al2O3/SiO2 ratio and the values of Cp. Further investigation is needed to develop stronger relationships, taking into account the effect of catalyst structure and intrinsic properties on the specific heat capacities of these catalytic materials.