**Acknowledgements**

Other kind of porous ceramics materials have been investigated for hydrocarbons gases detection. For instance, Picasso et al. [65] have produced sensors based on nanoparticles of

 doped with different amounts of Pd ranging from 0.1 to 1.0 wt.% for liquefied petroleum gas (LPG) detection. They demonstrated that the sample of Pd-doped sensors showed much higher sensitivity than the undoped one revealing the promotion electronic effect of Pd2+ on the surface reaction. Among all samples, the sensor with 0.75 wt.% Pd presented the highest gas response at 300°C in all gas tested concentrations, likely due to the highest BET surface, well-defined hematite crystalline structure and best surface contact over Pd surface via electronic mechanism. On the other hand, Xiaoqing Li et al. [29] produced mesoporous NiO NWs by using SBA-15 silica as the hard templates with the nanocasting method under the calcination temperature between 550 and 750°C. All results showed that all samples exhibited the best response to ethanol gas. The specific surface area decreased with the increasing calcination temperature, while crystallization degree and bandgap increased. Owing to the suitable specific surface area, crystallization degree and bandgap at the calcination temperature of 650°C, mesoporous NiO NWs-650 exhibited the best gas-sensing performance. For

nanoneedle arrays were successfully fabricated via a facile two-step

)0.5(OH)·0.11H<sup>2</sup>

. The highest sensitivity reached ∼89.6 for 100 ppm

O followed by

, etha-

, among others.

α-Fe<sup>2</sup> O3

ethanol detection Co<sup>3</sup>

66 Recent Advances in Porous Ceramics

**6. Conclusion**

nol (C<sup>2</sup>

H6

O), methanol (CH<sup>3</sup>

O4

indicating a great niche for future researches.

thermal conversion to mesoporous Co<sup>3</sup>

approach, including the formation of needle-shaped Co(CO<sup>3</sup>

O4

In addition, some of the most sensing materials used for humidity conditions are based on metal oxides, spinel- and perovskite-type oxides and/or thereof combination. Basically, the physicochemical properties of these materials allow them to detect humidity in gaseous media. The sensing mechanism of ceramic humidity sensors is based on water adsorption on the ceramic surface. The microstructure of these ceramic materials integrated by grains, porous, and their crystalline or non-crystalline phases support the sensing mechanism process. Hence, these kinds of sensors are based on the mechanical or electrical change due to bulk and/or surface modifications of the sensing materials with water adsorption [102]. Finally, the present state-of-art indicates that there are just a few publications related to the sensing hydrocarbons and/or their associated gases at low temperature and high humidity

In the recent past, a great deal of research efforts were directed toward the development of advanced ceramics porous materials due to their sensing properties and potential application for sensing hydrocarbons and/or their associated gases leaks. Among the various techniques that are available for gas detection, solid state metal oxides offer a wide spectrum of materials and their sensitivities for different gaseous species, making it a better choice over other options. The oxides that are covered in this study include oxides of aluminum, silicon, bismuth, cerium, chromium, cobalt, copper, indium, iron, nickel, niobium, tin, titanium, tungsten, vanadium, zinc, zirconium, and the mixed or multi-component metal oxides. The

cover hydrocarbons and their associated gases are liquefied petroleum gas (LPG), CH<sup>4</sup>

H6 O), H<sup>2</sup>

, NH<sup>3</sup>

, CO, H<sup>2</sup>

S, NO<sup>x</sup>

OH), acetone (C<sup>3</sup>

ethanol vapor and the optimal working temperature was as low as 130°C [87].

Dr. Y.A. Perera-Mercado is grateful to the West Houston Center for Science and Engineering Center (WHC) at Houston Community College System (HCCS); and Dr. G. Castruita-de Leon is thankful to Cátedras-CONACYT for the support received from both organizations in order to write this book chapter. Finally, the publication charges for this article have been funded by a grant from the publication fund of UiT The Arctic University of Norway.
