NH3 Adsorption Research Articles

Adsorption of hazardous gases on Cyclo[18]carbon and its analogues

Density functional theory calculations were performed to study the adsorption behavior of hazardous gases (NH3, CO2, CO, and NO) on twelve adsorbents (cyclo[18]carbon (C18) and its analogues Al9N9, B9N9, C6B6N6, C12B3N3, C14B2N2, d-C14B2N2, C16BN, C17Si; cyclo[12]carbon (C12) and its analogues Al6N6 and B6N6). The molecular electrostatic potential (MESP) maps of C18 revealed its polyynic structure with alternating electron-rich and electron-deficient regions. The most negative-valued MESP point (Vmin) indicates that the replacement of carbon atoms of C18/C12 by BN/AlN/Si units increases the electron-rich environment in the molecules. In general, NH3 and CO2 are found to be physisorbed on C18/C12 and its analogues. An important result is that the Vmin of C18/C12 and its analogues is linearly correlated with the NH3 and CO2 adsorption energies. The quantum theory of atoms in molecules (QTAIM) results indicate that the interactions of NH3 and CO2 with C18/C12 and its analogues are non-covalent in nature. In general, CO and NO are found to be chemisorbed on C18/C12 and its analogues. In contrast to the cases of NH3 and CO2 adsorption, the Vmin of C18/C12 and its analogues is generally inversely related to the CO and NO adsorption energies. The QTAIM results indicate the strong covalent character of the bonding for CO/C18, CO/C6B6N6, CO/d-C14B2N2, CO/C12, NO/C18, NO/C17Si, and NO/C12 systems. The adsorption process significantly influenced the chemical potential and/or hardness, especially for CO– and NO-adsorbed C18/C12 and its analogues.

Revealing the crystal-plane effects of CuO during the NH3-SCR over CuO/TiO2 catalysts

Copper-based (Cu-based) catalysts have garnered significant attention for their potential in ammonia-selective catalytic reduction (NH3-SCR) of nitrogen oxides (NOx). However, the widespread industrial application of Cu cation-exchanged chabazite catalysts has been hindered by poor hydrothermal stability, expensive raw materials, and complicated preparation. As a result, copper oxide-based (CuO-based) catalysts have emerged as ideal candidates due to their low cost and facile preparation. Nevertheless, the performance of NH3-SCR catalysts is a significantly influenced by the crystal plane effect, which has been scarcely investigated in Cu oxide-based NH3-SCR catalysts. In this study, CuO with exposed {001} and {111} facets were synthesized and combined with titanium dioxide (TiO2) support to construct CuO/TiO2 composite NH3-SCR catalysts. These catalysts displayed divergent NOx removal performance due to the crystal-plane effects of CuO. Specifically, the proportion of Cu+ and surface-adsorbed oxygen (Oα) in CuO(111)/TiO2 catalyst was higher than that of CuO(001)/TiO2 catalyst, which could facilitate the NH3-SCR reactions. The NH3-TPD, NO-TPD, and DFT calculations demonstrated the better NH3 and NO adsorption capability of CuO(111)/TiO2 catalyst than that of CuO(001)/TiO2 catalyst. Furthermore, the more -NH2 and nitrate species in CuO(111)/TiO2 catalyst resulted in better NOx removal efficiency than CuO(001)/TiO2 catalyst. This study provides fundamental insights on the crystal-plane effect of CuO, which is critical for optimizing Cu oxide-based NH3-SCR catalysts.

Influence of vacancy defects on 2D BeN4 monolayer for NH3 adsorption: a density functional theory investigation

Two-dimensional materials have attracted a great deal of interest in developing nanodevices for gas-sensing applications over the years. The 2D BeN4 monolayer, a recently synthesized single-layered Dirac semimetal, has the potential to function as a gas sensor. This study analyzes the NH3 sensing capacity of the pristine and vacancy-induced BeN4 monolayers using first-principles density functional theory (DFT) calculations. As per the results, the NH3 molecule is physisorbed on the pristine BeN4 via weak Van der Waals interaction with a poor adsorption energy of −0.41 eV and negligible charge transfer. Introducing Be vacancy in BeN4 increased the NH3 adsorption energy to −0.83 eV due to the improved charge transfer (0.044 e) from the defective monolayer to the NH3 molecule. The structural stability, sufficient recovery time (74 s) at room temperature, and superior work function sensitivity promise the potential application of defective BeN4 as an NH3 sensor. This research will be a theoretical groundwork for creating innovative BeN4-based NH3 gas sensors.

Optimization of Ni-amine coordination for improving NH3 permeation through nickel-doped bis[3-(trimethoxysilyl)propyl] amine membranes

Nickel-coordinated bis[3-(trimethoxysilyl)propyl] amine (BTPA) xerogels and membranes reportedly showed excellent NH3 adsorption, permeance, and permselectivity. To study the H2, N2, and NH3 permeation properties of Ni-BTPA membranes in detail, the nickel doping amount in BTPA should be optimized. In this work, Ni-BTPA sols/gels with nickel/propylamine (Ni/N–H) mole ratios of 0, 0.125, 0.25, 0.50, and 1.00 were prepared and characterized via DLS, FT-IR, UV–vis, TG-MS, and XRD, indicating that the sol size and the interactions between nickel and N–H/N=O were increased with an increase in the Ni/N–H mole ratio. The large NH3 adsorption and desorption amounts were obtained with 0.50 and 1.00 Ni-BTPA xerogels via NH3-TPD measurement, additionally, the competitive interactions between nickel and NH3/other functional groups, such as N–H and N=O, were found in 1.00 Ni-BTPA, which could negatively affect the NH3 affinity. The pore sizes of membranes were gradually enlarged in Ni-BTPA with increases in the nickel content, which improved gas permeation. Due to the enlargement of the pore size and the sufficient NH3 affinity, the 0.50 Ni-BTPA membrane recorded the optimal performance with a NH3 permeance of ∼ 2.8 × 10-6 mol m−2 s−1 Pa−1, an ideal NH3/H2 selectivity of 11, and NH3/N2 selectivity of 102 at 200 °C.

Nitrogen configuration dependent gas sensing performance based on nitrogen contained covalent organic polymers and frameworks

Gas sensing was a very important strategy to detect toxic and harmful gases, which was discharged into atmosphere. N-contained groups had been confirmed an important adsorption sites for target molecules in gas sensing process. Herein, we designed four N-contained groups in different configurations, including primary amine, secondary amine, tertiary amine and quaternary ammonium, to verify their difference in sensing performance. These four N-contained groups were embedded in four covalent organic polymers/frameworks through reasonable designation of building blocks. The sensing results indicated that primary amine, secondary amine and tertiary amine were excellent NH3 adsorption sites and beneficial for NH3 sensing. For 100 ppm NH3, the response value, response/recovery time were − 62%, 24 s/202 s for Amino-COP sensor, were − 51%, 18 s/173 s for Caz-COP sensor, and were − 76%, 19 s/206 s for CTF sensor at room temperature. The estimated LOD were 10 ppb for Amino-COP, 76 ppb for Caz-COP and 7.5 ppb for CTF, respectively. In contrast, quaternary ammonium was mainly NO2 adsorption site and could be applied in NO2 sensing. The response value, response/recovery time were − 76%, 76 s/264 s for Vio-COF to 100 ppm NO2. And the low LOD of 1.1 ppb was observed on Vio-COF sensor. Density functional theory (DFT) calculation and in-situ UV-Vis experiments confirmed that NH3 was interacted with primary amine, secondary amine, and tertiary amine through hydrogen bonding ways, while NO2 interacted with quaternary nitrogen atoms through coordination.

Mechanism study of Na poisoning on Ce/TiO2(001) surface based on adsorption of reaction species and elementary reaction pathways

The presence of alkali metal Na in flue gas can significantly impair the reactivity of Ce/TiO2 (CT) SCR (Selective Catalytic Reduction) catalyst. This study investigates the deactivation mechanism of Na on the Ce/TiO2 catalyst using Density Functional Theory (DFT) calculations, focusing on the adsorption of surface species and the pathway of elementary reaction. Due to the high affinity between Na atom and the catalyst surface, Na poisoning readily occurs on Ce/TiO2 (001) surface. The presence of Na on the catalyst surface hampers hydrogenation, oxygen vacancy formation, and NH3 adsorption, while also reducing the catalyst's acidity and reducibility. Additionally, Na impedes the NH3 dehydrogenation reaction, as well as the formation and decomposition of NH2NO and the dissociation of O2 on the catalyst surface, thereby inhibiting the NH3-SCR reaction. The inhibition of NO2 formation further affects the fast SCR reaction, which may explain the low-temperature deactivation of the catalyst.

Enhanced low-temperature performance of Al-rich Cu-SSZ-13 by Ce modification upon hydrothermal aging for NH3-SCR

3wt.% Cu/SSZ-13 (Cu3/Z) and Ce modified 3wt.% Cu/SSZ-13 (Ce-Cu3/Z) catalysts were prepared and then hydrothermally aged. The Ce-modified Ce-Cu3/Z catalyst revealed excellent NH3-SCR activity and hydrothermal stability. Combined with a series of characterizations, it was proved that the introduction of Ce could inhibit the dealumination, and prevent the aggregation of Cu ions to form CuOx and CuAl2O4 species upon hydrothermal aging, thus improving the hydrothermal stability of Ce-Cu3/Z. In addition, Ce could interact with Cu species to enhance the reducibility of catalyst, and the interaction between Ce and Cu species was strengthened after hydrothermal aging. Also, the presence of Ce species could enhance the NH3 and NOx adsorption capacity of the catalyst, resulting in higher NH3-SCR activity of Ce-Cu3/Z after hydrothermaly aged at 700 °C. In situ DRIFTS results showed that the NH3-SCR reaction followed both E-R and L-H mechanisms on the Cu3/Z-700 and Ce-Cu3/Z-700 catalysts at 150 °C. Ce doping could promote the formation of L-NH3 (NH3 species coordinated to Lewis acid sites) and nitrate species on the Ce-Cu3/Z-700 catalyst, as well as the involvement of L-NH3 in the reaction, which play a crucial role as the main active intermediates at low temperature.

Exploring Metal Nanocluster Catalysts for Ammonia Synthesis Using Informatics Methods: A Concerted Effort of Bayesian Optimization, Swarm Intelligence, and First-Principles Computation.

This paper details the use of computational and informatics methods to design metal nanocluster catalysts for efficient ammonia synthesis. Three main problems are tackled: defining a measure of catalytic activity, choosing the best candidate from a large number of possibilities, and identifying the thermodynamically stable cluster catalyst structure. First-principles calculations, Bayesian optimization, and particle swarm optimization are used to obtain a Ti8 nanocluster as a catalyst candidate. The N2 adsorption structure on Ti8 indicates substantial activation of the N2 molecule, while the NH3 adsorption structure suggests that NH3 is likely to undergo easy desorption. The study also reveals several cluster catalyst candidates that break the general trade-off that surfaces that strongly adsorb reactants also strongly adsorb products.

Simultaneous Generation of Ammonia during Nitrile Waste Gas Purification over a Silver Single-Atom-Doped Ceria Catalyst.

Catalytic elimination of toxic nitrile waste gas is of great significance for preserving the atmospheric environment, but achieving resource utilization during its destruction has been less explored. Herein, this study proposed a universal strategy for nitrile waste gas purification and NH3 generation simultaneously. The developed silver single-atom-doped ceria nanorod (Ag1/R-CeO2) was endowed with near complete mineralization and around 90% NH3 yield at 300-350 °C for the catalytic oxidation of both acetonitrile and acrylonitrile. The introduction of the Ag single atom created more surface oxygen vacancies, thereby promoting water activation to form abundant surface hydroxyl groups. As a benefit from this, the hydrolysis reaction of nitrile to generate NH3 was accelerated. Meanwhile, the electron transfer effect from the Ag atom to Ce and hydroxyl species facilitated NH3 desorption, which inhibited the oxidation of NH3. Moreover, the increased surface oxygen vacancies also promoted the mineralization of hydrolysis carbonaceous intermediates to CO2. In contrast, the Ag nanoparticle-modified sample possessed stronger reducibility and NH3 adsorption, leading to the excessive oxidation of NH3 to N2 and NOx. This work provided a useful guidance for resourceful purification of nitrile waste gas.

A promising catalyst for catalytic oxidation of chlorobenzene and slipped ammonia in SCR exhaust gas: Investigating the simultaneous removal mechanism

As the emission limits for NOx become further stringent, development of a synergistic control technology to prevent emissions of slipped ammonia (NH3) and chlorinated organics from steel production and waste incineration is both a prospect and a challenge for the environmental issues. In this work, the designed ruthenium-based catalyst (RuNb/ST) showed the excellent chlorobenzene (CB)/NH3 synergistic removal performance and N2/CO2 selectivity above 300 ℃. The activity of NH3 and CB were suppressed at relatively low temperature due to the competitive adsorption of CB and NH3. Whereas, there was a significant improvement in the N2/CO2 selectivity at relatively high temperature. The removal mechanism was studied by experiments, in which the accumulation of chlorine species, the role of NO2 and the oxidation of CB were considerable. In contrast to the carrier, the vast majority of the chloride ions adsorbed onto the active sites after dissociating from CB could be efficiently removed in form of Cl2 via the Deacon Reaction catalyzed by RuO2. CB was predominantly converted into CO2 and H2O with a fraction persisting as organics. Partial of organics were attacked by Cl ions to generate organic chlorine-containing by-products. The presence of NO2 molecule was found to promote the cleavage of the benzene ring within CB, and expedited the carbon migration towards the ultimate product of CO2, resulting in a notable reduction of byproducts.

Room-temperature flexible ammonia sensor based on SnO2 quantum dots modified graphene oxide

Tin dioxide quantum dots (SnO2 QD) were prepared by hydrothermal method, and then SnO2 QD modified graphene oxide (SnO2 QD@GO) was synthesized by a secondary hydrothermal technique to fabricate a flexible sensor for detecting ammonia at room temperature. The morphology, structure and composition of the composites were analyzed by SEM, TEM, EDS, XPS, XRD and Raman spectroscopy. TEM images showed that SnO2 QD with a diameter range of 5–8 nm present a cuboid structure, embedded in the two-dimensional GO surface. The gas sensing test shows that at room temperature the response of SnO2 QD@GO to ammonia is 5 times higher than that of GO. At the same time, the operating temperature of pure SnO2 QD is greatly reduced from 250 °C to room temperature (24 °C) by the composing of GO. Flexibility test of SnO2 QD@GO was also measured to test the fatigue resistance and bending test of the device. The improved ammonia sensing performance of SnO2 QD@GO is mainly due to the smaller bond energy of ammonia and abundant functional groups of GO, which provides more active sites for the surface adsorption of NH3.

Transformation of waste battery cathode material LiMn2O4 into efficient ultra-low temperature NH3-SCR catalyst: Proton exchange synergistic vanadium modification

It is essential to develop the catalyst for NH3-SCR with excellent performance at ultra-low temperature (≤150 °C), and resource recycling is another important part of environmental protection. Based on the principle of environmental friendliness, the LiMn2O4, one of the waste battery cathode materials, was successfully modified into a novel high-value catalyst for ultra-low temperature NH3-SCR through hydrogen ion exchange and two-dimensional vanadic oxide modification. The optimized LiMn2O4-0.5V-10H catalyst performed the best balance of NOx conversion and N2 selectivity, with activity reaching 96 % at 150 °C and N2 selectivity exceeding 70 % at ultra-low temperature. Due to the unique three-dimensional network structural characteristics of LiMn2O4 spinel, hydrogen exchange could exchange Li+ from the lattice and increase surface acidity; and a small amount of two-dimensional vanadic oxide loading could appropriately regulate redox ability and increase acidic sites. The in-situ DRIFTS results still showed that the L-H and E-R mechanisms coexisted during the reaction. Moreover, combining first-principles calculations and in-situ DRIFTS, the dual modification of H and V could enhance the adsorption of NH3 on the surface of LiMn2O4 but weaken the adsorption of NO, and promote the decomposition of nitrites while inhibit the formation of surface nitrate species, which was the core reason for the improvement of N2 selectivity. The modification mode in this work was simple and inexpensive, which provided a new idea for the high-value utilization of waste batteries and the design of NOx purification catalyst at ultra-low temperature.

Efficient NH3-Tolerant Nickel-Based Hydrogen Oxidation Catalyst for Anion Exchange Membrane Fuel Cells.

Converting hydrogen chemical energy into electrical energy by fuel cells offers high efficiencies and environmental advantages, but ultrapure hydrogen (over 99.97%) is required; otherwise, the electrode catalysts, typically platinum on carbon (Pt/C), will be poisoned by impurity gases such as ammonia (NH3). Here we demonstrate remarkable NH3 resistivity over a nickel-molybdenum alloy (MoNi4) modulated by chromium (Cr) dopants. The resultant Cr-MoNi4 exhibits high activity toward alkaline hydrogen oxidation and can undergo 10,000 cycles without apparent activity decay in the presence of 2 ppm of NH3. Furthermore, a fuel cell assembled with this catalyst retains 95% of the initial peak power density even when NH3 (10 ppm)/H2 was fed, whereas the power output reduces to 61% of the initial value for the Pt/C catalyst. Experimental and theoretical studies reveal that the Cr modifier not only creates electron-rich states that restrain lone-pair electron donation but also downshifts the d-band center to suppress d-electron back-donation, synergistically weakening NH3 adsorption.

Investigation of BN modified graphene nanoribbon for gas adsorption applications: DFT study

Graphene nanoribbons that are modified using boron and nitrogen (CBN) are examined in this work for their adsorption of CO, CO2, H2, H2O, NH3, NO, and NO2 gases. A first principles approach that utilizes density functional theory (DFT) computation is employed to investigate both perfect and vacancy defected structures. The gas molecule adsorption capacity is examined in this work by determination of the adsorption energy (Ed), adsorption length (D), charge exchanged amongst the gas and CBN (ΔQ), along with the density of states (DOS). The results indicate that NO and NO2 gases have favorable adsorption on the perfect CBN, however, chemisorption is not achieved for these gases. On the other hand, NO2 and NH3 gases have favorable adsorption on the vacancy defected CBN and they establish chemical bonds with the structure. Ed is 235% and 165% for NO2 and NH3, respectively, higher for the vacancy defected nanoribbon relative to the perfect nanoribbon. Furthermore, the adsorption length of NO2 and NH3 decreases dramatically for the vacancy defected CBN to 1.55 and 1.69 Å, while the charge transferred increases to 0.326 and -0.415 e, respectively. The sensor response evaluation indicates that the vacancy defected CBN structure exhibits an enhanced response towards NO2 gas followed by that of NH3. Consequently, the introduction of a vacancy defect in the CBN structure is an efficient approach to enhance its sensitivity and selectivity, particularly, for NO2 and NH3.

Enhanced catalytic behavior of La2O2CO3/Co3O4 composite for thermal decomposition of ammonium perchlorate

In this work, La2O2CO3, Co3O4 and La2O2CO3/Co3O4 composites were prepared by one-step solution combustion with citric acid as oxidant and lanthanum nitrate and cobalt nitrate as reductants. Morphology analysis showed many pores of different sizes on the surface of the composite. The best catalytic performance was for the La2O2CO3/Co3O4 composite. The high-temperature decomposition (HDT) of ammonium perchlorate (AP) decreased by 187.7 °C, and the activation energy decreased from 371.6 to 140.6 kJ mol−1. The combustion process of AP/hydroxyl-terminated polybutadiene solid propellant containing La2O2CO3/Co3O4 was more intense, the ignition delay time was shortened from 30 to 25 ms and the time to reach maximum combustion effect was advanced from 370 to 190 ms. Through the mechanism analysis, we believe that the adsorption of NH3 by La2O2CO3 promotes AP decomposition and also causes breakage of N–H bonds, which accelerates the oxidative decomposition of NH3. The Co3O4 has unfilled 3d orbitals, which could accelerate electron transfer during the reaction. At the same time, the interface between the two substances leaks more active sites, further accelerating electron transfer. Therefore, La2O2CO3/Co3O4 composites are expected to be widely used in solid propellants.

Excellent NH3-SCR activity and significant sulfur resistance over novel core–shell Cu-SSZ-13@meso-CeO2 catalyst

A core–shell Cu-SSZ-13@meso-CeO2 catalyst with both microporous and mesoporous pores was successfully synthesized using a self-assembly technique in this research. The catalyst was tested via NH3–SCR of NOx removal from diesel exhausts. The Cu-SSZ-13@meso-CeO2 catalyst was found to have significantly improved activity at high temperatures, wider temperature range, improved hydrothermal stability, and anti-sulfur performance. After the introduction of meso-CeO2, a significant synergistic effect between the Cu2+/Ce4+ ions on the core–shell layer was observed, and the amounts of Cu2+–2Z species and acidic sites increased, which may be conducive to the superior catalytic performance of Cu-SSZ-13@meso-CeO2 contrasted to Cu-SSZ-13. Subsequent to hydrothermal treatment, Cu-SSZ-13@meso-CeO2 maintains a superior CHA-type structure, additional L-acidic sites, and isolated Cu2+ ions while being protected by a meso-CeO2 shell. In addition, in the presence of SO2, the meso-CeO2 shell in Cu-SSZ-13@meso-CeO2 reacts with SO2 to produce cerium sulfate, which serves as a protective component for the copper species on Cu-SSZ-13. Moreover, the reaction mechanism studies have indicated that NO reduction primarily adheres to the E–R mechanism on Cu-SSZ-13, whereas both L–H and E–R mechanisms contribute to Cu-SSZ-13@meso-CeO2. SO2 has a less significant inhibitive effect on the adsorption of NH3 over Cu-SSZ-13@meso-CeO2 compared with that over Cu-SSZ-13. The inhibitive influence of SO2 on Cu-SSZ-13@meso-CeO2 is primarily owing to the inhibitory adsorption of NO and the reduction of the L–H reaction path, with little effect on the E–R reaction mechanism, which is significantly affected in Cu-SSZ-13. The Cu-SSZ-13@meso-CeO2 catalyst demonstrated exceptional NH3–SCR performance, a broad temperature range, and super hydrothermal stability as well as anti-sulfur performance, indicating great application prospects for NOx removal from diesel vehicle exhausts.

Evaluation of passive flux samplers with different orifice sizes to measure ammonia volatilization losses

AbstractA common passive sampler used to measure NH3 volatilization losses in field studies has a nozzle with a 1‐mm, round orifice that reduces air flow to increase NH3 adsorption. This reduction in air flow, measured by the orifice's K value (0–1), implies a reduction in the amount of NH3 entering the sampler per unit of time, which may require a longer exposure to accumulate measurable quantities of NH3. Increasing the diameter of the orifice would increase the NH3 entering the sampler and possibly allow shorter exposure times, but it may also lead to increased NH3 bypass. The objectives of this research were to (1) determine the effect of wind speed on NH3 bypass in samplers with 1‐ or 2‐mm orifices, (2) determine the reduction in air speed in samplers with 1‐ or 2‐mm orifices by determining their K values, and (3) compare field NH3 volatilization losses measured with 1‐ and 2‐mm orifices. A laboratory study with wind speeds ranging from 0.6 to 10 m·s−1 showed that both orifice sizes had NH3 bypass at low and high wind speeds. Results from wind tunnel studies determined that flow was reduced to 63% (K = 0.63) in 1‐mm orifices and to 74% (K = 0.74) in 2‐mm orifices. Field studies indicated that 1‐mm orifices may measure greater NH3 volatilization losses than 2‐mm orifices at average low wind speeds when maximum wind speeds <10 m·s−1, but may measure equal or lower losses than 2‐mm orifices when several days occur with maximum wind speeds >10 m·s−1.

Activated biocarbons obtained from lignocellulosic precursors as potential adsorbents of ammonia

The investigated materials were new biocarbons: FC (Fir Cone), FS (Fir Sawdust), FB (Fir Bark), BS (Birch Sawdust), BB (Birch Bark), AS (Acacia Sawdust), AB (Acacia Bark), OS (Oak Sawdust), OB (Oak Bark), HS (Hornbeam Sawdust)) obtained via pyrolysis and CO2 activation of wood waste (lignocellulosic biomass). In order to study the influence of the carbon precursor on the physicochemical properties of biocarbons there were used the precursors: cones, sawdust, and bark of various tree species. The obtained adsorbents were characterized based on the results, of the N2 adsorption, scanning electron microscopy (SEM), elemental analysis (CHNS), thermogravimetry (TG), derivative thermogravimetry (DTG), and differential thermal analysis (DTA), Fourier Transform Infrared Spectroscopy FT-IR (ATR) and the Boehm’s titration method as well as pHpzc (the point of zero charge). The adsorption capacity and the temperature-programmed desorption (TPD) of ammonia were also studied. The obtained activated biocarbons were characterized by the large specific surface area (515 to 1286 m2/g) and the total pore volume (0.27 to 0.46 cm3/g) as well as the well-developed microporous structure (76 - 90%). The maximum NH3 adsorption capacity of the activated biocarbon was determined to be 2.93 mmol/g (FC (Fir Cone)). These results prove that the lignocellulosic precursors are appropriate for preparation of environmentally friendly and cost-effective biocarbons.

Influence of oxidative conditions on the deactivation of an equilibrium FCC catalyst in the fast pyrolysis of HDPE in a conical spouted bed reactor

This study approaches the continuous catalytic fast pyrolysis of plastics in a flexible and original technology, i.e., a conical spouted bed reactor equipped with fountain confiner and draft tube. The catalyst is an inexpensive equilibrium fluid catalytic cracking (FCC) one. Moreover, operation under oxidative conditions is proposed to solve heat supply to the pyrolysis reactor, as a previous study revealed a remarkable difference in the performance of the cracking catalyst when pyrolysis was carried out under inert (conventional) and oxidative conditions. Therefore, the aim of this paper is to assess the role played in the catalyst stability and deactivation mechanism by the presence of air in the reaction environment. A comparative study has been conducted by operating in long continuous runs under the same conditions (550 °C and a space time of 15 gcatalyst min gHDPE−1) in inert and oxidative atmospheres, i.e., equivalence ratios (ER) of 0 and 0.2, respectively. The evolution of product distribution with time on stream was evaluated. Moreover, samples of catalysts were taken from the reactor at different reaction times to correlate catalyst performance with the deactivated catalyst properties, and therefore progress in the understanding of the deactivation mechanism. The amount and nature of the coke deposited on the catalyst and its influence on catalyst properties was ascertained using thermogravimetry (TG-TPO), Raman spectroscopy, and NH3 and N2 adsorption–desorption techniques. The operation under oxidative conditions improved product distribution, with higher yields of light olefins. Moreover, catalysts activity and stability were also enhanced under oxidative conditions. Therefore, the results obtained involve a step forward towards the scaling up of plastics continuous catalytic pyrolysis.

DFT investigation of metal-decorated silicon carbide nanosheets for the adsorption of NH3

The threat that ammonia (NH3) poses in various human activity environments drives the necessity of sensors of higher sensitivity. Two-dimensional (2D) materials have attracted attention for this particular purpose, with 2D silicon carbide being one prospect for this application. However, this potential use has been relatively unexplored. In this work, we study the adsorption of NH3 on pristine and metal (Li, Na, Mg, Ca, Ag, Au, Cu, Pd, and Ti) decorated silicon carbide monolayers (2D-SiC) using a first-principles approach based on Density-Functional Theory. Energetic analyses were performed to determine the enhancement or deterioration of the NH3 adsorption capacities of the 2D-SiC. The results show that the Ag- and Au-decorated monolayers are the best candidates for NH3 capturing due to the large adsorption energies found in these systems.