A review of chemical kinetic mechanisms and after-treatment of amino fuel combustion

Ammonia is a highly promising carbon-neutral fuel. The use of ammonia as a fuel for internal combustion engines can reduce fossil energy consumption and greenhouse gas emissions. However, the high ignition energy required for ammonia and the slow flame propagation rate result in low combustion efficiency when ammonia is used directly in internal combustion engines. The combination of ammonia with highly reactive fuels improves combustion quality and increases efficiency. However, the combustion of these combined fuels generates particulate matter, CO, hydrocarbon, and significant amounts of NOx. Therefore, pollutant emissions must be reduced through after-treatment technologies. In this paper, a series of combustion and post-treatment challenges faced by amino fuel combustion in internal combustion engines are extensively discussed and the combustion reaction mechanisms of different amino fuels are also analyzed. The paper then reviews five key technologies applicable to the reprocessing of amino fuels, including selective catalytic reduction, selective catalytic reduction filter technology, electrochemical methods for NOx removal, direct catalytic decomposition of N2O, and ammonia sliding catalysts. An in-depth discussion of the catalytic materials and reaction mechanisms involved in these technologies is also provided in this paper. Finally, the paper summarizes the main technical challenges that must be addressed for the future application of amino fuels in internal combustion engines. These discussions can serve as an essential reference for developing and applying critical technologies for combustion control and pollutant treatment of amino fuels.

Product Selection Toward High-Value Hydrogen and Bamboo-Shaped Carbon Nanotubes from Plastic Waste by Catalytic Microwave Processing

The escalating levels of plastic waste and energy crises underscore the urgent need for effective waste-to-energy strategies. This study focused on converting polypropylene wastes into high-value products employing various iron-based catalysts and microwave radiative thermal processing. The Al-Fe catalysts exhibited exceptional performance, achieving a hydrogen utilization efficiency of 97.65% and a yield of 44.07 mmol/g PP. The gas yields increased from 19.99 to 94.21 wt % compared to noncatalytic experiments. Furthermore, this catalytic system produced high-value bamboo-shaped carbon nanotubes that were absent in other catalysts. The mechanism analysis on catalytic properties and product yields highlighted the significance of oxygen vacancies in selecting high-value products through two adsorption pathways. Moreover, the investigation examined the variations in product distribution mechanisms between conventional and microwave pyrolysis, in which microwave conditions resulted in 4 times higher hydrogen yields. The technoeconomic assessment and Monte Carlo risk analysis further compared the disparity. The microwave technique had a remarkable internal rate of return (IRR) of 39%, leading to an income of $577/t of plastic with a short payback period of 2.5 years. This research offered sustainable solutions for the plastic crisis, validating the potential applicability of commercializing the research outcomes in real-world scenarios.

Potassium regulating electronic state of zirconia supported palladium catalyst and hydrogen spillover for improved acetylene hydrogenation

High-selectivity acetylene hydrogenation to produce ethylene is an important issue of removing acetylene impurity in ethylene for industrial polyethylene production. Developing high-efficiency catalyst with excellent ethylene selectivity and catalytic durability is desirable but still challenging. In this work, potassium doped palladium catalysts supported on zirconia with different K contents (Pd/ZrO2-xK) have been developed to catalyze acetylene hydrogenation, the Pd/ZrO2-16K exhibits impressive catalytic performance with acetylene conversion of 100 %, ethylene selectivity of 81 % and high catalytic durability. In situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS), in situ synchrotron radiation photoionization mass spectrometry (SR-PIMS) and density functional theory (DFT) calculations reveal that K doping effectively weakens the adsorption of ethylene by regulating the electronic state of catalyst to improve ethylene selectivity and substantially lowers the barriers of hydrogen activation and transfer reactions to favor hydrogen spillover, thus conferring a remarkably improved durability on the Pd/ZrO2-16K catalysts.

On the Catalytic Mechanism of 3d and 4d Transition-Metal-Based Materials on the Hydrogen Sorption Properties of Mg/MgH2

The slow hydrogenation/dehydrogenation kinetics and high thermodynamic stability of the Mg–H bond are the two major limitations for the large-scale utilization of MgH2. In this review, we introduce the catalytic mechanism of 3d and 4d transition metal (TM) on the hydrogen sorption properties of Mg/MgH2. The relative contribution of interatomic interactions to the thermodynamic stability of the TM-substituted MgH2 system is discussed. A synergy effect between the electronegativity and the radius of the TM element is proposed to explain the charge transfer process between TM and H in the TM-substituted MgH2 system. The catalytic mechanism of TM nearby the surface of Mg is more complicated than that in the volume of Mg, as the surface-doped TM can experience more options for doping sites, leading to the hindrance effect and causing various contributions of the d band center to the dissociation of hydrogen molecules and the diffusion of hydrogen atoms nearby the surface of Mg. In terms of the catalytic mechanism of TM for hydrogen sorption kinetics of Mg/MgH2, we particularly focused on the “hydrogen pump” effect existing in the Mg–TM–H system. Other mechanisms, such as a possible catalytic mechanism of TM for the hydrogen sorption properties of nano-sized freestanding Mg/MgH2, were also presented.

Revealing hydrogen spillover pathways in reducible metal oxides

Hydrogen spillover, the migration of dissociated hydrogen atoms from noble metals to their support materials, is a ubiquitous phenomenon and is widely utilized in heterogeneous catalysis and hydrogen storage materials. However, in-depth understanding of the migration of spilled hydrogen over different types of supports is still lacking. Herein, hydrogen spillover in typical reducible metal oxides, such as TiO₂, CeO₂, and WO₃, was elucidated by combining systematic characterization methods involving various in situ techniques, kinetic analysis, and density functional theory calculations. TiO₂ and CeO₂ were proven to be promising platforms for the synthesis of non-equilibrium RuNi binary solid solution alloy nanoparticles displaying a synergistic promotional effect in the hydrolysis of ammonia borane. Such behaviour was driven by the simultaneous reduction of both metal cations under a H₂ atmosphere over TiO₂ and CeO₂, in which hydrogen spillover favorably occurred over their surfaces rather than within their bulk phases. Conversely, hydrogen atoms were found to preferentially migrate within the bulk prior to the surface over WO₃. Thus, the reductions of both metal cations occurred individually on WO₃, which resulted in the formation of segregated NPs with no activity enhancement.

The hydrogen spillover pathway in typical reducible metal oxides, such as TiO₂, CeO₂, and WO₃, was investigated by combining various in situ characterization techniques, kinetic analysis, and density functional theory calculations.

H-spilled storage to maximize the catalytic performances of Pd-based bimetals@Ti3C2Tx MXene in selective semihydrogenations

Hydrogen spillover is an important theme for hydrogen storage and H-involving catalytic reactions. This work shows that catalytic reactivity and selectivity can be revealed by differentiating energetic characteristics of the...

SO2 Resisting Pd-doped Pr1-x Cex MnO3 Perovskites for Efficient Denitration at Low Temperature

H₂ -SCR is served as the promising technology for the controlling of NO_x emission, and the Pd-based derivative catalyst exhibited high NO_x reduction performance. Effectively regulating the electronic configuration of the active component is favorable to the rational optimization of noble Pd. In this work, a series of Pr_1-x Ce_x Mn_1-y Pd_y O₃ @Ni were successfully synthesized and exhibited superior NO conversion efficiency at low temperatures. 92.7 % conversion efficiency was achieved at 200 °C over Pr_0.9 Ce_0.1 Mn_0.9 Pd_0.1 O₃ @Ni in the presence of 4 % O₂ with a GHSV of 32000 h^-1 . Meanwhile, the outstanding performance was obtained in the resistance to SO₂ (200 ppm) and H₂ O (8 %). Deduced from the results of XRD, Raman, XPS, and H₂ -TPR, the modification of d orbit states in palladium was confirmed originating from the incorporation in the B site of Pr_0.9 Ce_0.1 Mn_0.9 Pd_0.1 O₃ . The existence of higher valence (Pd³⁺ and Pd⁴⁺ ) than the bivalence in Pr_0.9 Ce_0.1 Mn_0.9 Pd_0.1 O₃ catalyst was evidenced by XPS analysis. Our research provides a new sight into the H₂ -SCR through the higher utilization of Pd.

A promising Al-CeZrO4/HPW-incorporated SPEEK composite membrane with improved proton conductivity and chemical stability for PEM fuel cells

An improved sulfonated poly (ether ether ketone) (SPEEK) nanocomposite membrane was prepared by incorporating both phosphotungstic acid (HPW) and Al doped cerium-based oxides (Al-CeZrO4) in SPEEK matrix. The HPW was immobilized by Al-CeZrO4 so that firmly dispersed acid–base pairs were formed. The introduction of Al-CeZrO4 helped improve the chemical stability of the pristine (baseline) SPEEK membrane without compromising the conductivity, and the addition of HPW further enhanced the conduction of protons through acid–base interactions. Stability tests showed that when the SPEEK/Al-CeZrO4 nanocomposite membrane was immersed in a Fenton’s solution for 108 h at 80°C, a loss of 34.9% in proton conductivity was observed, which is 24.1% less than that of the pristine SPEEK membrane, indicating that the attenuation of membrane proton conductivity was inhibited. At the same time, the proton conductivity of the SPEEK/Al-CeZrO4/HPW nanocomposite membrane (that has already incorporated HPW) was increased by 15.5% compared to the SPEEK/Al-CeZrO4 nanocomposite membrane. Hence, Al-CeZrO4/HPW is considered as an effective inorganic nanofiller for improving both proton conductivity and chemical stability of SPEEK membranes, and the hybrid composite membrane is worth further studying.

Double signal amplification based on palladium nanoclusters and nucleic acid cycles on a μPAD for dual-model detection of microRNAs

Dual-model signal outputs and double signal amplification on the platform of μPAD for the sensitive detection of miRNAs.