## 1 Introduction  
Several sources of clays are available in the Saudi Arabia, and so numerous studies have been conducted to characterize them and to investigate their potential uses [1; 2; 3; 4; 5; 6]. Saudi Arabia is geologically divided into four distinct and extensive terrains, (Figure S1). Al-Hasa oases are situated between the rock desert of As Summan plateau in the west and sand dunes covering the adjoining plain in the east. As shown in Figure S1 in Supplementary Information (SI), Al-hasa is one of the largest oases in the world (534,000 km\({}^{2}\)), situated between 25\({}^{\circ}\)05\({}^{\prime}\) and 25\({}^{\circ}\)40\({}^{\prime}\) northern latitude and 49\({}^{\circ}\)55\({}^{\prime}\) eastern longitude. To the best of our knowledge, no extensive study has been conducted to investigate the surface and physicochemical characteristics of Al-Hasa clays and their potential uses in the literature.  
It is well known that clays are widely used in many industrial applications such as ceramic, paper, paint, barrier, catalyst, and adsorbent applications, etc. [7; 8; 9]. Reuse of wastewater resources from industrial processes is a strategic aim in Saudi Arabia. On the other side, heavy metals, especially lead, are the common contaminants of wastewater, collected as residues from petroleum industries. Clays are known to be used as alternative cheap materials for removal of heavy metals. So, five clay samples were collected from parent soil in different geographical regions of Al-Hasa in Saudi Arabia (viz., Tabuk, Baha and Khaiber) and tested in lead removal from wastewater [2].  
On the other hand, the worldwide demand for ethylene and propylene has been growing steadily. Methanol-to-hydrocarbon conversion reactions were first discovered in the early 1970s using ZSM-5 (MFI zeolite) catalysts [10; 11]. Different catalytic systems have been considered for use in methanol to olefin reactions, including an acid-type ion exchange resin, aluminum phosphate, a mesoporous silica alumina, e.g., Al-MCM41 or Al-MCM48, a zeolite, or a lamellar zeolite [12]. Regarding the natural clay-based catalysts for the methanol conversion processes, acidic clay mineral (e.g., kaolin or leached kaolin, etc.) or clay modified with acid such as sulfuric acid or phosphoric acid [10; 11; 12] could be used. Among all these catalytic systems, natural clays are the cheapest solids. Thus, in the present study, Al-Hasa clays were also investigated in the dehydration of methanol, following their catalytic performances.  
Generally, the suitability of clay for a specific application is based on its mineralogical composition, crystal morphology, porosity, surface area, surface acidity and thermal stability [13]. Therefore, the main objective of this research work was to characterize the collected clay samples (Figure S2) via various techniques: X-ray powder diffraction (XRD), scanning electron microscopy (SEM), N\({}_{2}\) adsorption, thermogravimetric analysis (TGA) as well as potentiometric acid-base titration. An attempt was undertaken to investigate the different catalytic performances of these clays in the removal of lead contaminant and in the selective methanol conversion to ethylene, in relation to the various characterization parameters. The study was also extended to explore the effect caused by the coexistence of different minerals in the clay (viz., palygorskite, montmorillonite, calcite) on the mechanism of lead adsorption profiles.