Thermal Catalytic Process Research Articles

Enabling Sustainable Ammonia Synthesis: From Nitrogen Activation Strategies to Emerging Materials.

Ammonia (NH3) is one of the most important precursors of various chemicals and fertilizers. Given that ammonia synthesis via the traditional Haber-Bosch process requires high temperatures and pressures, it is critical to explore effective strategies and catalysts for ammonia synthesis under mild reaction conditions. Although electrocatalysis and photocatalysis can convert N2 to NH3 under mild conditions, their efficiencies and production scales are still far from the requirements for industrialization. Thermal catalysis has been proven to be the most direct and effective approach for ammonia synthesis. Over the past few decades, significant efforts have been made to develop novel catalysts capable of nitrogen fixation and ammonia generation via thermal catalytic processes. In parallel with catalyst exploration, new strategies such as self-electron donation, hydride fixation, hydridic hydrogen reduction, and anionic vacancy promotion have also been explored to moderate the operating conditions and improve the catalytic efficiency of ammonia synthesis. In this review, the emergence of new materials and strategies for promoting N2 activation and NH3 formation during thermal catalysis is briefly summarized. Moreover, challenges and prospects are proposed for the future development of thermal catalytic ammonia synthesis.

Plasma-Enabled Process with Single-Atom Catalysts for Sustainable Plastic Waste Transformation.

In this study, we present a novel plasma-enabled strategy for the rapid breakdown of various types of plastic wastes, including mixtures, into high-value carbon nanomaterials and hydrogen. The H2 yield and selectivity achieved through the catalyst-free plasma-enabled strategy are 14.2 and 5.9 times higher, respectively, compared to those obtained with conventional thermal pyrolysis. It is noteworthy that this catalyst-free plasma alone approach yields a significantly higher energy yield of H2 (gH2/kWh) compared to other pyrolysis processes. By coupling plasma pyrolysis with thermal catalytic process, employing of 1 wt.% M/CeO2 atomically dispersed catalysts can further enhance hydrogen production. Specifically, the 1 wt.% Co/CeO2 catalyst demonstrated excellent catalytic performance throughout the 10 cycles of plastic waste decomposition, achieving the highest H2 yield of 46.7 mmol/gplastic (equivalent to 64.4% of theoretical H2 production) and nearly 100% hydrogen atom recovery efficiency at the 7th cycle. Notably, the H2 yield achieved over the atomically dispersed Fe on CeO2 surface in the integrated plasma-thermal catalytic process is comparable to that obtained with Fe particles on CeO2 surface (10 wt.%). This innovative and straightforward approach provides a promising and expedient strategy for continuously converting diverse plastic waste streams into high-value products conducive to a circular plastic economy.

Electrocatalytic Acetylene Hydrogenation in Concentrated Seawater at Industrial Current Densities.

Electrocatalytic acetylene hydrogenation to ethylene (E-AHE) is a promising alternative for thermal-catalytic process, yet it suffers from low current densities and efficiency. Here, we achieved a 71.2 % Faradaic efficiency (FE) of E-AHE at a large partial current density of 1.0 A cm-2 using concentrated seawater as an electrolyte, which can be recycled from the brine waste (0.96 M NaCl) of alkaline seawater electrolysis (ASE). Mechanistic studies unveiled that cation of concentrated seawater dynamically prompted unsaturated interfacial water dissociation to provide protons for enhanced E-AHE. As a result, compared with freshwater, a twofold increase of FE of E-AHE was achieved on concentrated seawater-based electrolysis. We also demonstrated an integrated system of ASE and E-AHE for hydrogen and ethylene production, in which the obtained brine output from ASE was directly fed into E-AHE process without any further treatment for continuously cyclic operations. This innovative system delivered outstanding FE and selectivity of ethylene surpassed 97.0 % and 97.5 % across wide-industrial current density range (≤ 0.6 A cm-2), respectively. This work provides a significant advance of electrocatalytic ethylene production coupling with brine refining of seawater electrolysis.

In-situ integration of potassium carbonate/Kraft lignin catalyst preparation and biodiesel production via ball-milling process

In this paper, an in-situ integration process of catalyst preparation and biodiesel production via ball-milling process was first proposed. The yield of biodiesel can reach 100 % in a short preparation time of 10 min and a reaction time of 20 min. According to the temperature tracking data during the reaction, there is a synergistic catalytic effect of mechanical energy and thermal energy in the reaction process. The characterization results showed the catalyst prepared by ball-milling process has excellent catalytic activity and potassium (K) is uniformly dispersed on ball-milling-K2CO3/Kraft lignin (BM-K2CO3/KL) catalysts. Based on socio-economic and techno-economic evaluation, biochar-derived catalyst for biodiesel production has created a good market value, and the mechanochemical processes are more cost-effective than traditional thermal catalytic process. This process uses ball-milling technology to integrate catalyst preparation and biodiesel production, which has the advantage of simple operation, strong controllability, and is conducive to improving the FAME yield.

Photoexcitation Altered Reaction Pathway Greatly Facilitate Ammonia Synthesis Over Isolated Ru Sites

AbstractAmmonia, poised as a carbon‐neutral energy carrier, holds immense promise in reshaping the future energy landscape. Despite the enduring importance of the Haber–Bosch process in ammonia production, its substantial carbon emissions and energy demands necessitate more sustainable pathways. Here, an advanced ammonia synthesis route, enhanced by photoexcitation is demonstrated, which fundamentally modifies the activation pathways of N2 molecules. This alteration significantly lowers the reaction activation energy, resulting in remarkably improved reaction efficiency. The impact of light excitation culminates in an unprecedented ammonia synthesis rate of 18 mmol g−1 h−1, surpassing the traditional thermal catalytic process by 2.57‐fold. More importantly, light assistance reduces the thermal energy input by ≈16%, making it comparable to thermal catalysis while substantially improving energy utilization. This work introduces a greener strategy for ammonia synthesis, pushing the century‐old fossil‐fueled Haber–Bosch process to a new frontier.

Pnictocatalysis

Abstract2D materials based on Group 15 elements (pnictogens) have appeared during the last ten years, with a rich surface chemistry characterized by a plethora of dangling electron pairs, ready to interact with outer molecules. These molecular interactions enable catalytic properties beyond any external electro‐ or photo‐stimulus. In analogy with carbocatalysis, defined as thermal catalytic processes over extended carbon surfaces (graphene, nanotubes, etc.), we propose here the term “pnictocatalysis”, defined as thermal catalytic processes over extended pnictogen surfaces (which include phospho‐, arsene‐, antimony‐ and bismuth‐catalysis). Pnictocatalysis consitutes a new field in catalysis, with unexplored latent reactions to be encountered. In this minireview, we show the few examples found to date (not more than ten), which mark the pathway to find new pnictocatalyzed reactions, not exclusive with two‐dimensional (2D) materials but also with other pnictogen nanostructures.

Experimental investigation of the plasma-assisted spray combustion of methanol/water mixtures

To achieve the goal of net zero by 2050, carbon dioxide emissions must be reduced using carbon–neutral fuels, and methanol is a feasible choice for gas turbines, IC engines, and furnaces. Methanol can be prepared by bio-process or thermal catalytic processes, but the crude product contains much water. Crude methanol must be dehydrated into high-grade methanol to enable its use as fuel. The dehydration process is the most energy-intensive step in methanol production. Therefore, this study investigated the feasibility of adding different proportions of water to methanol as a fuel for plasma-assisted spray combustion by using low-power gliding arc plasma. Based on the current sprayer setup, using plasma to sustain water-content methanol is more energy-efficient than refining it. The results delineate that plasma can sustain the combustion of methanol in a spray, even when the methanol contains 60 % water. The length and lift-off height of the flame are related to the water content of the fuel. To illustrate this distinguishing phenomenon, this study used CH and OH fluorescence to conduct a more in-depth analysis. The distribution of CH* radicals indicated that the gliding arc plasma enhanced the flame heat release rate, which may be why the flammability limit extended to greater proportions of water with methanol. It's fascinating to observe that blended fuel with higher water content can result in higher OH chemiluminescence signals. This suggests that the dissociation of water vapor, caused by the thermal effect of the gliding arc, plays a crucial role at the flame base locations. In addition, the flammability limits, emissions, and combustion efficiency of methanol/water spray combustion with and without plasma assistance were all examined.

Searching for the Rules of Electrochemical Nitrogen Fixation.

Li-mediated ammonia synthesis is, thus far, the only electrochemical method for heterogeneous decentralized ammonia production. The unique selectivity of the solid electrode provides an alternative to one of the largest heterogeneous thermal catalytic processes. However, it is burdened with intrinsic energy losses, operating at a Li plating potential. In this work, we survey the periodic table to understand the fundamental features that make Li stand out. Through density functional theory calculations and experimentation on chemistries analogous to lithium (e.g., Na, Mg, Ca), we find that lithium is unique in several ways. It combines a stable nitride that readily decomposes to ammonia with an ideal solid electrolyte interphase, balancing reagents at the reactive interface. We propose descriptors based on simulated formation and binding energies of key intermediates and further on hard and soft acids and bases (HSAB principle) to generalize such features. The survey will help the community toward electrochemical systems beyond Li for nitrogen fixation.

Electrochemical splitting of methane in melts: Producing and tuning high-value carbon materials with controllable morphology

Catalytic decomposition of methane offers a viable solution for producing pure hydrogen and nanocarbon without emitting carbon dioxide. However, conventional thermal catalytic processes and catalysts have limitations in terms of poor carbon quality and catalyst deactivation due to carbon deposition. The newly developed electrochemical splitting of methane (ESM) in molten salt has emerged as a promising alternative that allows for the separate production of hydrogen at the anode and carbon deposition at the cathode. In this study, hydrogen produced via ESM while generating nanocarbon with diverse structures through manipulations of the cathode material and kinetics. Carbon nanotubes grown on Ni cathode, possessing high specific surface area and abundant functional groups, displayed excellent adsorptive capacity for dye adsorption. The open hollow nanocarbon grown on the Ag cathode displayed good capacitance performance. ESM technology has immense potential to enhance the utilization value of carbon by-products and the commercial production of green hydrogen.

Zn Promotes Chemical Looping Ammonia Synthesis Mediated by LiH-Li2 NH Couple.

Chemical looping ammonia synthesis (CLAS) is a promising alternative route to ammonia production because of its advantages of avoiding competitive adsorption of N2 and hydrogen source (H2 O or H2 ) and intervening the scaling relations in the catalytic process. Our previous studies showed that NH3 can be synthesized at low temperatures via a CLAS mediated by an alkali or alkaline earth metal hydride-imide couple with the aid of transition metal catalysts. Herein, we demonstrate that a group-IIB metal Zn, which has rarely been studied in the thermal-catalytic process, can significantly promote the performance of the lithium hydride-lithium imide (LiH-Li2 NH)-mediated CLAS process (denoted as Zn-LiH-Li2 NH). The addition of Zn dramatically changes the reaction pathway of the LiH-Li2 NH mediated loop by forming a series of intermediates including Li2 NH, lithium zinc intermetallic compounds (LiZnx ), and a ternary metal nitride (LiZnN). LiZnN together with Li2 NH functions as nitrogen carrier in the Zn-LiH-Li2 NH-mediated CLAS. Because of these properties, the kinetics of N2 fixation is significantly enhanced with a reduction in apparent activation energy from 102 kJ mol-1 to 50 kJ mol-1 . The ammonia production rate reaches 956 μmol g-1 h-1 at 350 °C, which is 19 times higher than that of the neat LiH-Li2 NH-mediated CLAS.

Harnessing Solar Energy Towards Synergistic Photothermal Catalytic Oxidation of Volatile Organic Compounds

Volatile organic compounds (VOCs) are prominent air pollutants, hazardous to human health and the environment. Sunlight is a sustainable energy source capable of meeting the demands for heterogeneous catalysis. Photothermal catalysis has emerged as an energy‐efficient technology for VOCs oxidation by merging the advantages of thermochemistry and photocatalysis. This review examines the advantages of the photothermal catalytic system, such as the absorption and conversion of solar light, accelerated reaction rates, and improved product selectivity. The photothermal catalytic system is clearly categorized according to the significant contributions of light and thermal energy to the reaction. As a result of the direct conversion of photons into thermal energy to surpass the light‐off temperature and drive the catalytic reaction, an ample discussion of light‐induced thermal catalytic processes is presented. Furthermore, the participation of the localized surface plasmon resonance effect and oxygen vacancies in the surface reaction under irradiation and thermal energy are spotlighted. A comprehensive discussion is provided for the various photothermal active nanostructures. The underlying superior resistance mechanism to water vapour and coke formation as well as high oxygen concentrations in photothermal catalytic system are emphatically highlighted. Finally, current research trends and prospects are discussed.

In Situ Modification of CuO-Fe2O3 by Nonthermal Plasma: Insights into the CO2-to-CH3OH Hydrogenation Reaction.

The hydrogenation of CO2 to CH3OH on the binary mixed metal oxides of CuO-Fe2O3 under nonthermal plasma discharge has been reported in this study. The catalysts are synthesized using the sol-gel route and characterized by XRD, FTIR, SEM, and XPS techniques. The impact of CuO mixing with Fe2O3 on CO2 conversion and CH3OH yield has been investigated. Herein, we have compared two distinct techniques, namely thermal and plasma catalytic processes. The overall outcome shows that the CO2 conversion and CH3OH production increase with an increase in CuO mixing with Fe2O3. The synthesized catalyst does not show significant CO2 conversion and CH3OH formation in the thermal catalytic process (100-250 °C). Interestingly, when plasma discharge is combined with thermal heating, CO2 conversion and CH3OH production significantly improve. The plasma discharges in the CO2/H2 gas stream, at low temperatures (<200 °C), reduce Cu+2 to Cu+1 and Fe+3 to Fe+2, which could probably enhance the CO2 conversion and CH3OH production. Among the catalysts prepared, 15% CuO-Fe2O3 exhibited the best catalytic activity with 13.2% CO2 conversion, 7.3% CH3OH yield, and a space-time yield of 13 mmolCH3OH/h gcat, with 4.67 kJ/L of specific input energy (SIE). The CH3OH space-time yield is 2.9-fold higher than that of the commercial catalyst Cu/ZnO/Al2O3, which is operated at 30 °C with 45.45 kJ/L SIE.

Role of Hydride Formation in Electrocatalysis for Sustainable Chemical Transformations

The electrochemical potential of numerous reduction reactions corresponds to hydrogen pressures that thermodynamically favor the formation of many metal hydrides. Whether a catalyst remains metallic with hydrogen on the surface (Hads) or absorbs hydrogen into its lattice (Habs), forming a metal hydride, results from a balance between not only this thermodynamic driving force but also the kinetics of concurrent surface reactions and equilibrium surface coverage. Drawing parallels with thermal catalytic processes, we provide examples of how hydride formation impacts electrocatalysis in H2 evolution, organic and CO2 reduction, and N2 and NO3– reduction reactions. Hydride formation not only changes catalyst activity and selectivity but also can impact durability. We highlight techniques capable of identifying hydride formation under reaction conditions, imperative for an understanding of electrocatalyst kinetics. Hydrides offer many possibilities in electrocatalysis, including unique reaction mechanisms involving the catalyst lattice and innovative reactor architectures, beneficial for applications in chemical transformations and energy.

Carbon capture and utilization: More than hiding CO2 for some time

Carbon capture and utilization: More than hiding CO2 for some time

2,5-Diformylfuran production by photocatalytic selective oxidation of 5-hydroxymethylfurfural in water using MoS2/CdIn2S4 flower-like heterojunctions

The selective oxidation of 5-hydroxymethylfurfural (HMF) into 2,5-diformylfuran (DFF) is an important reaction for renewable biomass building blocks. Compared with thermal catalytic processes, photocatalytic production of DFF from HMF has attracted tremendous attention. Herein, the MoS 2 /CdIn 2 S 4 (MC) flower-like heterojunctions were prepared and considered as photocatalysts for selective oxidation of HMF into DFF under visible-light irradiation in aqueous solution. Results demonstrated MoS 2 in MC heterojunction could promote the separation of photoexcited electron-hole pairs, while the amount of MoS 2 dropping was proved influenced on the photocatalytic performance. 80.93% of DFF selectivity was realized when using 12.5% MC as photocatalyst. In addition, the MC catalyst also showed great potential in transformation of other biomass derived benzyl- and furyl-alcohols. The catalytic mechanism suggested that · O 2 - was the decisive active radical for HMF oxidation. Therefore, the MC heterojunction could be applied in photocatalytic conversion of biomass to valuable chemicals under ambient condition.

Promoted Photothermal Catalytic CO Hydrogenation by Using TiC-Supported Co-Fe5 C2 Catalysts.

Photothermal catalytic CO hydrogenation offers the potential to synthesize light hydrocarbons by using solar energy. However, the selectivity and activity of the reaction are still far below those achieved in conventional thermal catalytic processes. Herein, we report that the Co-modified Fe5 C2 on TiC catalyst promotes photothermal catalytic CO hydrogenation with a 59 % C2+ selectivity in the produced hydrocarbons and a 30 % single-pass CO conversion at a high gas hourly space-time velocity of 12 000 mL g-1 h-1 . Using in-situ-irradiated XPS, we show that light-induced hot electron injection from TiC to Fe5 C2 modulates the chemical state of Fe, thereby increasing the CO-to-C2+ conversion. This work suggests that it is possible for plasmon-mediated surface chemistry to enhance the activity and selectivity of photothermal catalytic reactions.

Economic Analysis of Thermal–Catalytic Process of Palm Oil (Elaeis guineesensis, Jacq) and Soap Phase Residue from Neutralization Process of Palm Oil (Elaeis guineensis, Jacq)

Palm oil is, from an economic, environmental, and social point of view, a vegetable oil with great potential and the state of Pará-Brazil is Brazil’s great producer. In addition, soap phase residue or palm oil neutralization sludge (PONS), a byproduct of the neutralization step of the chemical refinement of palm oil, is produced, posing a huge problem for waste disposal and management in the production process of refined palm oil (RPO). In this context, this work aims to systematically investigate the economic analysis of the thermal–catalytic process of crude palm oil (CPO) and palm oil neutralization sludge (PONS). The thermocatalytic processes of CPO and PONS carried out at pilot scale and their economic feasibility were analyzed. The yields of biofuels produced by fractional distillation were also presented. The physicochemical properties of CPO and PONS, as well as those of organic liquid products obtained by the thermal–catalytic process of CPO and PONS were taken into account in the economic analysis. In addition, the chemical composition organic liquid products obtained by thermal–catalytic process of CPO and PONS, as well as its distillation fractions (green gasoline, green kerosene, green light diesel and heavy diesel), used as key factors/indicators on the economic analysis. The analysis of the key factors/indicators from the thermocatalytic processes of CPO and PONS showed economic viability for both crude palm oil (Elaeis guineensis, Jacq) and palm oil neutralization sludge. The minimum fuel selling price (MFSP) obtained in this work for the biofuels was 1.59 USD/L using crude palm oil (CPO) and 1.34 USD/L using palm oil neutralization sludge (PONS). The best breakeven point obtained was of 1.24 USD/L considering the PONS. The sensibility analysis demonstrated that the pyrolysis and distillation yields are the most important variables that affect the minimum fuel-selling price (MFSP) in both economic analyses.

UV–vis-enhanced photothermal catalytic reforming of biomass model tar via LaMnxNi1-xO3 perovskite catalyst

Tar formation during biomass gasification reduces energy efficiency and poses a negative impact on downstream applications. A photothermal steam reforming (PTR) system based on LaMnxNi1-xO3 (0 ≤ x ≤ 1) perovskite was developed to convert tar into combustible gas. The effects of Mn substitution, temperature, and the steam to carbon ratio on PTR activity were investigated. Mn substitution increased the content of surface adsorbed oxygen and maintained the perovskite structure of LaMn0.4Ni0.6O3 (LM4N6). Moreover, LM4N6 showed improved optical absorption and electron-hole separation properties. LM4N6 presented 90 % carbon conversion during PTR at 400 °C. Due to the introduction of ultraviolet–visible light (UV–vis), LM4N6 obtained better catalytic activity and stability in PTR than in the thermal catalytic reforming process. Detailed characterization and experiments proved that UV–vis effectively activated Ni sites and the oxygen species on LM4N6 and formed a photothermal synergistic effect, which inhibited carbon deposition and improved catalytic activity and stability. This work provides a novel concept for the conversion and utilization of biomass tar at low temperatures.

Economic Feasibility Assessment of the Thermal Catalytic Process of Wastes: Açaí Seeds (Euterpe oleracea) and Scum from Grease Traps

In this work, a techno-economic assessment of the production of bio-oil, coke and gas, via thermo-catalytic pyrolysis followed by distillation, is accomplished. The raw materials were two solid wastes: lipid-based material (residual fat/scum from a fat retention box from the University Restaurant at the Federal University of Pará—UFPA) and a lignin-cellulosic material of açaí seed (Euterpe oleracea Mart.). From the literature, a review is made of the physicochemical analysis of the raw materials, of the bio-oil, and of the chemical composition of the biofuels produced (kerosene, light diesel, and heavy diesel). The bio-oil yields for each experiment of pyrolysis and distillation are also presented and compared with the literature. The economic indicators for the evaluation of the most viable cracking (pyrolysis) and distillation process of bio-oils were: (a) the simple payback criterion, (b) discounted payback, (c) net present value (NPV), (d) internal rate of return (IRR), and (e) index of profitability (IP). The analysis of the indicators showed the economic viability of the lipid-based material and unfeasibility for the açai seed (Euterpe oleracea Mart.). The breakeven point obtained was 1.28 USD/L and the minimum fuel selling price (MFSP) obtained in this work for the biofuels was 1.34 USD/L). The sensibility analysis demonstrated that the pyrolysis and distillation yields are the most important variables to affect the minimum fuel selling price (MFSP).

Recent Advances in Photocatalytic Oxidation of Methane to Methanol.

Methane is one of the promising alternatives to non-renewable petroleum resources since it can be transformed into added-value hydrocarbon feedstocks through suitable reactions. The conversion of methane to methanol with a higher chemical value has recently attracted much attention. The selective oxidation of methane to methanol is often considered a “holy grail” reaction in catalysis. However, methanol production through the thermal catalytic process is thermodynamically and economically unfavorable due to its high energy consumption, low catalyst stability, and complex reactor maintenance. Photocatalytic technology offers great potential to carry out unfavorable reactions under mild conditions. Many in-depth studies have been carried out on the photocatalytic conversion of methane to methanol. This review will comprehensively provide recent progress in the photocatalytic oxidation of methane to methanol based on materials and engineering perspectives. Several aspects are considered, such as the type of semiconductor-based photocatalyst (tungsten, titania, zinc, etc.), structure modification of photocatalyst (doping, heterojunction, surface modification, crystal facet re-arrangement, and electron scavenger), factors affecting the reaction process (physiochemical characteristic of photocatalyst, operational condition, and reactor configuration), and briefly proposed reaction mechanism. Analysis of existing challenges and recommendations for the future development of photocatalytic technology for methane to methanol conversion is also highlighted.