Utilizing Undissolved Portion (UNP) of Cement Kiln Dust as a Versatile Multicomponent Catalyst for Bioethylene Production from Bioethanol: An Innovative Approach to Address the Energy Crisis

This study focuses on upcycling cement kiln dust (CKD) as an industrial waste by utilizing the undissolved portion (UNP) as a multicomponent catalyst for bioethylene production from bioethanol, offering an environmentally sustainable solution. To maximize UNP utilization, CKD was dissolved in nitric acid, followed by calcination at 500 °C for 3 h in an oxygen atmosphere. Various characterization techniques confirmed that UNP comprises five different compounds with nanocrystalline particles exhibiting an average crystal size of 47.53 nm. The UNP catalyst exhibited a promising bioethylene yield (77.1%) and selectivity (92%) at 400 °C, showcasing its effectiveness in converting bioethanol to bioethylene with outstanding properties. This exceptional performance can be attributed to its distinctive structural characteristics, including a high surface area and multiple-strength acidic sites that facilitate the reaction mechanism. Moreover, the UNP catalyst displayed remarkable stability and durability, positioning it as a strong candidate for industrial applications in bioethylene production. This research underscores the importance of waste reduction in the cement industry and offers a sustainable path toward a greener future.


Characterization Techniques
The X-ray powder diffraction (XRD) analysis of the original CKD sample and the calcined samples at 500°C was conducted using a Brucker AXS-D8 Advance diffractometer (Germany).The instrument was equipped with a copper anode that generated Ni-filtered CuKa radiation (k = 1.5406Å) from a generator that operated at 40 kV and 40 mA, and the analysis was conducted in the 2θ range between 20°-80°.
The DIFFRACplus SEARCH and DIFFRACplus EVA interfaces were utilized to automatically search and match the crystalline phases with the COD crystallographic database for identification purposes.
The FTIR spectra were obtained using a Magna-FTIR 500 (USA) with Nicolet Omnic software and the KBr disk technique, and the spectra were recorded between 4000 and 250 cm -1 .
The prepared UNP sample was subjected to thermal analyses using thermogravimetric (TG) and differential scanning calorimetric (DSC) techniques.The experiments were conducted with a heating rate of 10°C.min - in 40 mL.min -1 N 2 -gas flow rate, using a 50H Shimadzu thermal analyzer-Japan.The instrument was equipped with a data acquisition and handling system (TA-50WSI), and highly sintered -Al 2 O 3 was used as a reference material in the DSC experiments.
The surface textural properties, including the specific surface area, pore volume, and mean pore radius of the UNP sample calcined at 500°C were determined 3S by analyzing nitrogen adsorption-desorption isotherms recorded at a temperature of liquid nitrogen (-196°C).This analysis was carried out using an automatic Micromeritics ASAP2010 (U.S.) equipped with online data acquisition and handling system operating BET and BJH analytical software.Prior to the measurements, all the samples were degassed at 200°C and 10 -5 Torr for two hours.To determine the total number of acidic sites (sites.g - ) on the UNP sample calcined at 500°C, temperature-programmed desorption (TPD) of tetrahydrofuran (THF) condensed phase was used.Prior to exposing the probe molecule (THF), 50 mg of the UNP sample was preheated at 350°C for 1 hour in air.About 20 mg of the sample covered with THF was subjected to thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) analyses at a heating rate of 10°C.min - in dry N 2 flowing at a rate of 40 ml.min -1 , using a 50H Shimadzu thermal analyzer from Japan.The thermal analyzer was equipped with a data acquisition and handling system (TA-50WSI), and -Al 2 O 3 was used as the reference material in DSC measurements.
(1 Torr = 133.3Pa).The morphological characterization of the UNP sample was performed using Scanning Electron Microscopy (SEM) with a FEI Quanta 250 FEG MKII, which had a high-resolution environmental microscope (ESEM) and XT microscope Control software.EDX dot mapping analysis combined with FESEM was employed to determine the homogeneous dispersion of sample constituents.SEM images of the UNP sample were obtained using a FEI Quanta 250 FEG MKII with a high-resolution environmental microscope (ESEM) and XT Microscope Control software linked to an Electron Dispersive X-ray (EDX) detector.The EDX detector that was used was a 10 mm 2 SDD Detector-x-act from Oxford Instruments, which utilized Aztec® EDX analysis software.The HR-TEM images were obtained using a JOEL JEM-HR-2100 electron microscope with 200 KV accelerating voltage and 400.00 Kx total magnification.XPS was collected on K-ALPHA ( Themo Fisher Scientific, USA) with monochromatic X-ray Al K-alpha radiation -10 to 1350 e.v spot size 400 micro at pressure 10-9 mbar with full spectrum pass energy 200 e.v and at narrow spectrum 50 e.v.

Table S1 .
The chemical composition of CKD obtained from Misr Cement-Qena Factory, expressed as weight percentage, was determined using x-ray fluorescence