Chemical fixation of CO2 conducted by Mg-based materials catalysts to produce cyclic carbonates: A comprehensive review

We are witnessing a surge in CO2 emissions into the atmosphere, leading to serious environmental issues for our planet. If we do not take action, it will harm humanity and the biosphere. Increased levels of CO2 in the atmosphere contribute to global warming, which results in climate upheavals that disrupt ecosystems, alter plant reproduction conditions, and cause numerous related problems. Consequently, the current CO2 levels in the atmosphere must be significantly lowered as soon as possible. CO2 is a plentiful C1 feedstock, and its chemical utilization has inspired chemists in recent years. The reaction of CO2 with epoxide to produce cyclic carbonate (CCs) is highly significant and actively pursued in laboratories worldwide. So, by chemically fixing CO2 into valuable cyclic carbonates, we can achieve two goals at once: reducing atmospheric CO2 and producing essential chemicals. However, CO2's low reactivity and high stability make fixation challenging, leading to the development of innovative heterogeneous catalytic systems to address this. Magnesium-based materials (Mg-based materials) have become an attractive choice for chemical catalysis of CO2 fixation reactions owing to their unique properties enabled by the polar structure of Mg(II) leads to their high CO2 affinity. This research deals with the introduction of Mg-based materials, synthesis methods, and their effect on the performance of the catalytic process in CO2 fixation reactions. Thus, this review can provide researchers with light horizons in utilizing the high potential of Mg-based materials in synthesizing efficient catalysts to achieve excellent yield, conversion, and selectivity in the cycloaddition of CO2 to epoxides into CCs.

The potential utility of dendritic fibrous nanosilica as an adsorbent and a catalyst in carbon capture, utilization, and storage

Anthropogenic emissions of greenhouse gases (GHG; e.g., CO2) are regarded as the most critical cause of the current global climate crisis. To combat this issue, a plethora of CO2 capture, utilization, and storage (CCUS) technologies have been proposed and developed based on a number of technical principles (e.g., post-combustion capture, chemical looping, and catalytic conversion). In this light, the potential utility of dendritic fibrous nanosilica (DFNS) materials is recognized for specific CCUS applications (such as adsorptive capture of CO2 and its catalytic conversion into a list of value-added products (e.g., methane, carbon monoxide, and cyclic carbonates)) with the highly tunable properties (e.g., high surface area, pore volume, multifunctional surface, and open pore structure). This review has been organized to offer a comprehensive evaluation of the approaches required for tuning the textural/morphological/surface properties of DFNS (based on multiple synthesis and modification scenarios) toward CCUS applications. It further discusses the effects of such approaches on the properties of DFNS materials in relation to their CCUS performance. This review is thus expected to help develop and implement advanced strategies for DFNS-based CCUS technologies.

Advanced zeolite and ordered mesoporous silica-based catalysts for the conversion of CO2 to chemicals and fuels

For many years, capturing, storing or sequestering CO₂ from concentrated emission sources or from air has been a powerful technique for reducing atmospheric CO₂. Moreover, the use of CO₂ as a C1 building block to mitigate CO₂ emissions and, at the same time, produce sustainable chemicals or fuels is a challenging and promising alternative to meet global demand for chemicals and energy. Hence, the chemical incorporation and conversion of CO₂ into valuable chemicals has received much attention in the last decade, since CO₂ is an abundant, inexpensive, nontoxic, nonflammable, and renewable one-carbon building block. Nevertheless, CO₂ is the most oxidized form of carbon, thermodynamically the most stable form and kinetically inert. Consequently, the chemical conversion of CO₂ requires highly reactive, rich-energy substrates, highly stable products to be formed or harder reaction conditions. The use of catalysts constitutes an important tool in the development of sustainable chemistry, since catalysts increase the rate of the reaction without modifying the overall standard Gibbs energy in the reaction. Therefore, special attention has been paid to catalysis, and in particular to heterogeneous catalysis because of its environmentally friendly and recyclable nature attributed to simple separation and recovery, as well as its applicability to continuous reactor operations. Focusing on heterogeneous catalysts, we decided to center on zeolite and ordered mesoporous materials due to their high thermal and chemical stability and versatility, which make them good candidates for the design and development of catalysts for CO₂ conversion. In the present review, we analyze the state of the art in the last 25 years and the potential opportunities for using zeolite and OMS (ordered mesoporous silica) based materials to convert CO₂ into valuable chemicals essential for our daily lives and fuels, and to pave the way towards reducing carbon footprint. In this review, we have compiled, to the best of our knowledge, the different reactions involving catalysts based on zeolites and OMS to convert CO₂ into cyclic and dialkyl carbonates, acyclic carbamates, 2-oxazolidones, carboxylic acids, methanol, dimethylether, methane, higher alcohols (C₂₊OH), C₂₊ (gasoline, olefins and aromatics), syngas (RWGS, dry reforming of methane and alcohols), olefins (oxidative dehydrogenation of alkanes) and simple fuels by photoreduction. The use of advanced zeolite and OMS-based materials, and the development of new processes and technologies should provide a new impulse to boost the conversion of CO₂ into chemicals and fuels.

Single-Atom Catalysts across the Periodic Table

Isolated atoms featuring unique reactivity are at the heart of enzymatic and homogeneous catalysts. In contrast, although the concept has long existed, single-atom heterogeneous catalysts (SACs) have only recently gained prominence. Host materials have similar functions to ligands in homogeneous catalysts, determining the stability, local environment, and electronic properties of isolated atoms and thus providing a platform for tailoring heterogeneous catalysts for targeted applications. Within just a decade, we have witnessed many examples of SACs both disrupting diverse fields of heterogeneous catalysis with their distinctive reactivity and substantially enriching our understanding of molecular processes on surfaces. To date, the term SAC mostly refers to late transition metal-based systems, but numerous examples exist in which isolated atoms of other elements play key catalytic roles. This review provides a compositional encyclopedia of SACs, celebrating the 10th anniversary of the introduction of this term. By defining single-atom catalysis in the broadest sense, we explore the full elemental diversity, joining different areas across the whole periodic table, and discussing historical milestones and recent developments. In particular, we examine the coordination structures and associated properties accessed through distinct single-atom-host combinations and relate them to their main applications in thermo-, electro-, and photocatalysis, revealing trends in element-specific evolution, host design, and uses. Finally, we highlight frontiers in the field, including multimetallic SACs, atom proximity control, and possible applications for multistep and cascade reactions, identifying challenges, and propose directions for future development in this flourishing field.