Hydrogen is considered an efficient alternative fuel. Most of the hydrogen produced on a large scale mainly comes from the steam reforming of natural gas, which is considered the most established and least expensive method. Although water electrolysis is also a well-established technique used to produce hydrogen, it causes high energy losses. The generation, storage, and transportation of hydrogen as an alternative fuel have been extensively studied during the last few decades. Given the challenges in generating and storing hydrogen for portable applications, ammonia has been proposed as an alternative for on-site hydrogen production through its decomposition. In this study, the catalytic decomposition of ammonia was conducted to produce CO₂-free hydrogen. Ru-based catalysts have been recognized as efficient catalysts for ammonia decomposition under mild reaction conditions. For Ru-based catalysts, the supports were found to play a profound role in the ammonia decomposition process. CeO₂ is an efficient support for ammonia decomposition, but as it is expensive, CeO₂ cannot be used for large-scale industrial applications. Therefore, Ru-based catalysts were prepared using CeO₂-impregnated Al₂O₃ supports. CeO₂-impregnated Al₂O₃ supports were prepared in various Ce/Al molar ratios. The catalysts prepared from CeO₂-impregnated Al₂O₃ supports with molar ratios of 0.5 and 1.0 showed a comparative efficiency to those prepared from a pure CeO₂ support. The presence of less expensive Al₂O₃ in bulk while achieving comparable efficiency to that of a pure CeO₂-supported Ru catalyst resulted in cost-effective and efficient catalysts for ammonia decomposition.

Introduction:
The contamination of water bodies by pharmaceutical pollutants, such as tetracycline, poses a significant environmental threat. Traditional water treatment methods often fall short in effectively removing these pollutants. This study investigates the synthesis of a novel Ceₓ-Mn-Tiᵧ@illite catalyst, designed for the efficient photocatalytic degradation of tetracycline in aqueous solutions.

Methods:
The catalyst was synthesized by impregnating illite, a natural clay, with varying concentrations of cerium (Ce), manganese (Mn), and titanium (Ti) ions. The synthesis process was characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy dispersive X-ray spectroscopy (EDX) to confirm the structural properties of the catalyst. Photocatalytic degradation experiments were carried out under UV light irradiation to evaluate the efficiency of tetracycline removal, with reaction parameters such as pH, catalyst dosage, and irradiation time varied to optimize performance.

Results:
The Ceₓ-Mn-Tiᵧ@illite catalyst showed significant photocatalytic activity, achieving a high degradation rate of tetracycline under optimal conditions. The catalyst demonstrated excellent stability and reusability over multiple cycles, maintaining its efficiency in pollutant removal. The reaction kinetics were analyzed, revealing that the degradation followed pseudo-first-order kinetics. The catalyst's efficiency was further enhanced by the synergistic effect of the metal dopants, which facilitated charge separation and improved photocatalytic performance.

Conclusions:
The Ceₓ-Mn-Tiᵧ@illite catalyst represents an effective and sustainable material for the removal of tetracycline from aqueous solutions. This study highlights the potential of clay-based catalysts in photocatalytic applications for environmental remediation. The results contribute to the development of cost-effective and eco-friendly materials for water treatment technologies, particularly for pharmaceutical pollutant degradation.

This thesis investigates the catalytic pyrolysis of low-density polyethylene (LDPE) that has been contaminated with limonene, a terpene that is commonly found in orange juice and used as a model contaminant. The selection of limonene is based on its high prevalence in natural products and its strong affinity for polyethylene, as evidenced by several studies. The research aims to evaluate the influence of limonene on the thermal and catalytic degradation of LDPE and to explore how its presence alters the pyrolysis process. Additionally, the effect of ZSM-5 zeolite, a widely used catalyst that is known for enhancing LDPE conversion into valuable hydrocarbons, is assessed.

In this study, low-density polyethylene (LDPE, DOW 310E) and d-limonene (Alfa Aesar) were used to examine the limonene sorption by LDPE. For each experiment, 3 g of LDPE pellets was divided into three aluminum supports (1 g per support) and placed in an airtight desiccator containing 12 mL of limonene in a beaker. The setup was incubated at 40°C, and sorption was monitored by weighing the LDPE after 12 days to determine the absorbed limonene, which ranged between 150 and 160 mg per gram of LDPE. Pyrolysis experiments were conducted at 450°C with a nitrogen flow rate of 200 mL/min.

The results show that limonene influences the distribution of the pyrolysis phases (gas, liquid, and solid), with the liquid fraction being analyzed via Gas Chromatography–Mass Spectrometry (GC-MS). The chemical transformations of the pure and absorbed limonene were also characterized using Fourier Transform Infrared Spectroscopy (FTIR). These findings provide insights into the role of contaminants such as limonene in shaping the efficiency and product distribution of catalytic pyrolysis, contributing to a better understanding of how to valorize contaminated polyethylene waste.

This work describes the generation of highly reactive Lewis pair sites on CuMo-oxides for CO₂ activation and utilization over the cyclization reaction to produce propylene carbonate from 1,2-propanediol. The CuMo-oxides were synthesized by enabling the oxygen vacancies that enhance the catalytically active sites, resulting in the formation of metastable cations (Mo⁵⁺ and Cu⁺) and oxygen vacancies. Under ethanol-PEG-400 medium, the pure phase of Cu₃Mo₂O₉ obtained at 500 °C exposed maximum defects without any secondary phase compared to the other screened catalysts. The experimental and theoretical investigations provided evidence for determining and correlating the characteristics of active sites with catalytic performance. The catalysts were extensively characterized along with DFT studies, which revealed the presence of defect centers as one of the key factors in the enhanced activity. From the chemical bonding analysis, i.e., the Crystal Orbital Hamiltonian Population (COHP) and Electron Localization Function (ELF), the CO₂ molecule is known to form a strong chemisorption interaction with the catalyst surface that is facilitated by the oxygen vacancy/Lewis pairs. The Cu-Mo oxide catalyst exhibited a better performance under optimal reaction conditions with a 1,2-propanediol conversion of 99% and propylene carbonate yield of 97% compared to the reported catalysts due to its inherent physicochemical properties. Thus, Cu-Mo oxides were shown to be highly efficient catalysts with good recyclability for the 1,2-propanediol and CO₂ reaction.

The utilization of CO₂ for the synthesis of value-added chemicals can help to reduce its concentration in the atmosphere [1]. The synthesis of 2-imidazolidinone using a nontoxic CO₂ as carbonyl source has drawn greater attention as CO₂ is abundant, which can be used as C1 feedstock for chemical synthesis [2]. In this study, a ZnO-supported hydroxyapatite (HAP) catalyst was designed based on the active sites required for this reaction. The Zn-HAP catalyst was synthesized by the one-step hydrothermal method. This supported catalyst showed better activity than support HAP and unsupported ZnO. Higher yield could be achieved by tuning the acid-base sites by varying the ZnO loading and calcination temperature. The catalyst was characterized using different techniques such as XRD, N₂ -sorption, SEM-EDS, TEM, XPS, CO₂ and NH₃-TPD to understand its structural and textural properties. It was found that the acidic and basic properties of the catalysts played vital roles in achieving better catalytic activity. The XPS analysis showed a decrease in the intensity of Ca 2p peaks of Zn-HAP as compared with HAP, indicating the replacement of Ca²⁺ by Zn²⁺ in the structure which results in generation of new active sites, leading to an enhanced catalytic activity. Design of experiment (DOE) was employed using response surface methodology (Central Composite Design) to optimize reaction conditions. The optimized catalyst was shown to be stable and reusable by achieving 81% of conversion for ethylene diamine and 97% selectivity for 2-imidazolidinone under moderate pressure and temperature in 10 hours. The catalyst also showed good versatility by giving good yield for the reaction between different types of amines and CO₂. The activity of the catalyst correlated well with its physicochemical properties.

Heavy metals are essential raw materials for the manufacture of industrial products, but they are one of the causes of environmental pollution and are harmful to human health. Due to their toxicity, the presence of heavy metals in water and food is strictly regulated. Graphite furnace atomic absorption spectrophotometry (GFAAS) is a widely used technique for heavy metal analysis because of the small sample volume required and a simple operating procedure involved. However, sensitivity at trace concentrations of analyte in the matrix is limited by physical and chemical interferences. Overcoming this limitation requires the preconcentration and separation of analytes.

In this study, a solid-phase extraction (SPE) method using activated carbon modified with stearic acid (SA-CAA) as an adsorbent was developed to preconcentrate cadmium and nickel ions in water samples. Different characterization methods were employed to confirm the structural and surface modifications of the studied absorbent. The results show that the stearic acid modification of activated carbon enhanced the interaction between the adsorbent and heavy metal ions, leading to an approximately twofold increase in recovery compared to unmodified activated carbon. The analytical parameters affecting recovery, including the adsorption time, amount of adsorbent, initial pH of the sample solution, desorbent conditions, and sample volume, were optimized. The analytical performance of the proposed method, such as the calibration curve, analytical precision, detection limit, and tolerance to interfering components, was evaluated.

Dyes are persistent and toxic pollutants that significantly contribute to water pollution, particularly from the textile and dye industries. Advanced oxidation processes (AOPs) have attracted considerable interest as they are believed to be effective in removing persistent and toxic organic pollutants from water by generating reactive oxygen species. In addition, NaBH₄ treatment is believed to enhance catalyst reactivity by generating abundant oxygen vacancies. This study explored the activation of peroxymonosulfate (PMS) and the decolorization of Reactive Yellow 86 using MnCo₂O₄ catalysts treated with NaBH₄.

The MnCo₂O₄ (MCO) catalyst was synthesized by hydrothermal and calcination methods followed by NaBH₄ treatment, yielding the modified catalyst MCO-1.25. The catalytic performance of MCO and MCO-1.25 was compared in decolorizing Reactive Yellow 86 in the presence of PMS. Specifically, 1 mg of catalyst was added to a vessel containing 10 mL of 50 mg/L Reactive Yellow 86 and 10 mL buffer solution and stirred for 30 min. After adsorption equilibrium was reached, 0.48 mM PMS solution was added to initiate the decolorization reaction. The solution was aliquoted at regular intervals, and the reaction was quenched by the addition of methanol. After centrifugation, the supernatant was measured in a spectrophotometer and the decolorization rate was determined from the measured absorbance.

With MCO, approximately 90% of Reactive Yellow 86 was decolorized after 30 min. In contrast, with MCO-1.25, approximately 100% was decolorized after 20 min. The enhanced performance of MCO-1.25 was attributed to the increased oxygen vacancies induced by the NaBH₄ treatment, resulting in improved PMS activation. These modifications improved the generation and utilization of reactive oxygen species, leading to faster and more efficient decolorization.

The presence of nitrogenated compounds in fossil fuels leads to NOx formation during combustion; these are harmful pollutants that pose significant environmental and health challenges. Hydrotreatment, the conventional strategy for denitrogenation, requires severe conditions, which motivates the search for more environmentally friendly alternatives. Oxidative denitrogenation (ODN) requires milder operating conditions and explores the oxidative reactivity of nitrogen compounds. In this study, cobalt ferrite (CoFe₂O₄) catalysts were synthesized and coated with silica (SiO₂) or carbon (C), and applied for the ODN of quinoline, common in fuels, using hydrogen peroxide as the oxidant.

The superparamagnetic CoFe₂O₄ (core) was synthesized using the sol–gel method and, using an adaptation of the Stöber method, further coated with SiO₂ or C (shell). Characterization techniques, such as XRD, FTIR, and contact angle measurements, confirmed the core–shell structure of the developed catalyst and showed a remarkable change in the ferrite’s hydrophobic surface properties upon coating (a decrease from 130° to 40° with silica). Crystallite sizes in the range of 19-20 nm were obtained.

Quinoline adsorption tests showed the low adsorption capacity of the materials, in accordance with the low surface area and pore volume determined by N₂ adsorption isotherms at 77 K (S_BET = 9-10 m² g^-1). In oxidation reactions, CoFe₂O₄@SiO₂ showed the best catalytic performance (X_QN = 74%, 8 h), likely ascribed to its hydrophilic surface, favorable to the generation of oxygen reactive species through the decomposition of H₂O₂ and consequent higher quinoline removal. Quinoline degradation was verified by GC-MS, which indicated the opening of the pyridine ring.

The results highlight that cobalt ferrite-based catalysts employed in oxidative denitrogenation are capable of degrading and mineralizing quinoline under mild conditions, as confirmed by TOC analyses. The surface properties of the coatings significantly increased the catalytic efficiency, emphasizing their potential as environmentally friendly and efficient candidates for the removal of nitrogen compounds from fossil fuels.

Growing environmental concerns have increased the focus on sustainable, biodegradable alternatives to plastic-based materials [1]. Among these, nanocellulose (NC) is valued for its renewability, biocompatibility, and functional properties, making it a promising candidate for diverse applications. NC is classified into cellulose nanocrystals (CNCs), cellulose nanofibrils (CNFs), and bacterial nanocellulose (BNC), each derived through distinct processes [2]. Plant-based nanocellulose (CNCs and CNFs) is typically produced through the depolymerization of lignocellulosic biomass to remove hemicellulose and amorphous cellulose fractions, retaining nanoscale crystalline cellulose. This is achieved enzymatically, chemically, or mechanically [2]. In contrast, BNC is synthesized via a polymerization-based process, where bacteria convert sugars into cellulose [3].

Inspired by these pathways, we developed a dual bioprocess that integrates both approaches using lignocellulosic biomass to valorize the streams. Agricultural and forest residual feedstocks were subjected to a mild OxiOrganosolv pretreatment process [4], producing a cellulose-rich solid fraction and a hemicellulose-rich aqueous liquor. Both streams underwent enzymatic hydrolysis and saccharification, with sugar release quantified using spectrophotometry and other methods. The fermentable sugars were then used as a carbon source for the microbial production of BNC by Komagataeibacter sp., and the resulting nanocellulose was characterized to confirm its properties. Optimizing the process with various biomass sources, enzymatic treatments, and bacterial strains directed the system toward enhanced saccharification (maximizing sugar release for BNC synthesis) or higher cellulose integrity retention (enhancing CNF yield) [5]. Different enzyme combinations were tested to balance these outcomes, and various carbon sources were evaluated for their effectiveness in supporting bacterial strains to optimize nanocellulose production yield. This integrated process offers a sustainable, scalable approach to NC production, maximizing output with minimal input.

Methane decomposition through chemical looping reforming (CLR) is emerging as a promising and innovative approach for hydrogen production. This method efficiently transforms various feedstocks into high-purity hydrogen while drastically reducing greenhouse gas emissions. Hydrogen generated through CLR represents an environmentally friendly option, free from direct emissions of air pollutants or greenhouse gases. Additionally, it supports the use of a diverse range of low-carbon energy sources, contributing to its sustainability and versatility. In particular, supported nickel-based catalysts show promising features due to their strong catalytic activity and stability in reforming processes. The present study focuses on the performance of Ni and Ru-Ni catalysts supported on LaMnO₃, synthesized through precipitation assisted by microwave irradiation and sol-gel citrate methods. The redox stability was checked by performing multiple redox cycles during chemical looping experiments carried out isothermally, alternating the gas composition every 10 minutes from 15 vol% of CH₄ in N₂ (reduction) to 15 vol% of CO₂ in N₂ (oxidation). The CLR temperature was selected for each sample based on temperature-programmed reduction tests with methane, choosing for each one the temperature of maximum reduction. Through a comprehensive examination encompassing structural, morphological, and catalytic analyses, it was possible to study the impact of synthesis techniques on the performance of these catalysts in hydrogen production via chemical looping decomposition. These research efforts furnish valuable insights pivotal for the development of efficient and sustainable processes and crucial for meeting the escalating demand for clean energy solutions in the contemporary era.