# Catalytic Evaluation of Hafnium Modified SiO\({}_{2}\) for the Dehydration of Alcohols
## 1 Introduction  
Since the discovery of mesoporous like MCM-41, MCM-48, HMS, and SBA-15, countless application possibilities have been opened for these materials in the field of heterogeneous catalysis, especially when metal atoms are introduced in the silicate structure, particularly organic and/or metallic species that promote interesting properties in silicates. In particular, textural properties are favored with increased specific area, uniform porosity, acidity, and thermal stability. These are some essential parameters that a solid material must meet for its application in catalytic reactions. The mesoporous silicate type MCM-41 meets these characteristics, with a hexagonal arrangement, surface area greater than 1000 m\({}^{2}\)/g, and pore size of about 20 A [1] facilitating the accessibility of bulky molecules to active sites and the rapid diffusion of reagents and products inside and outside the porous structure, leading to an increase in catalytic conversion which means a significant advantage over microporous materials, such as zeolites [2]. Nowadays, mesoporous silicates have been the subject of many studies to control their pore size, surface area, thermal stability, etc. However, their lack of acid sites limits their application as catalysts, but if a transition metal is introduced into the silicate structure, it generates a certain degree of acidity associated with the nature of the chemical bonds of the metal and silica [3]. Ti, Zr, Al, W, Mo, andCr are among the most studied metal ions, which provide acidity to silicates of the M41S family [4; 5; 6; 7; 8]. A few numbers of studies have reported the influence of hafnium on the structural properties and catalytic behavior of MCM-41-type silicates. Generally, these studies focus on developing dielectric and micro electrical devices due to good thermal and mechanical stability and interfacial compatibility of hafnium with silicon [9; 10; 11]. On the other hand, hafnium oxide (HfO\({}_{2}\)) shares physicochemical characteristics similar to those of zirconium oxide (ZrO\({}_{2}\)) [12; 13; 14]. [PERSON] et al. [15] reported that SO\({}_{4}^{2-}\) ions promote stability of the tetragonal phase of ZrO\({}_{2}\), so it is expected that HfO\({}_{2}\) will have the same behavior if SO\({}_{4}^{2-}\) ions are introduced into the silicate structure. [PERSON] et al. [16] reported that doping SiO\({}_{2}\) with cerium and hafnium oxide increases thermal stability, acidity and/or basicity of the solid material. The acid-base nature of this material was evaluated in the decomposition of 4-methyl-2-pentanol into light olefins.  
On the other hand, products from the dehydration of alcohols are a source of raw materials of high commercial value, such as light olefins and ethers that have been used as propellants, refrigerants, and fuels and could even be used as hydrogen sources for clean energy generation [17; 18]. The present study reports the modification of an MCM-41 type silicate with Hf and SO\({}_{4}^{2-}\) ions to promote acidity in the mesoporous silicate and its catalytic activity in the dehydration of alcohols.