Temperature-programmed Desorption Spectroscopy Research Articles

Fine-tuned MOF-74 type variants with open metal sites for high volumetric hydrogen storage at near-ambient temperature

Adsorbent-based hydrogen storage systems offer a potential solution to current challenges in hydrogen storage, particularly those requiring high pressures or cryogenic temperatures. Specifically, the use of metal–organic frameworks (MOFs) featuring open metal sites that strongly adsorb hydrogen represents a promising strategy for near-ambient-temperature hydrogen storage. This study investigates the hydrogen storage properties of M2(dondc) (M = Mg2+, Co2+, and Ni2+), an extended version of MOF-74. Among this series, Ni2(dondc) exhibits the second-highest volumetric hydrogen capacity of 10.74 g L−1 at 298 K under pressure swing adsorption conditions (100 to 5 bar) at ambient temperatures. The superior hydrogen storage performance of Ni2(dondc) is attributed to its highly polarizable Ni open metal sites and a significant heat of adsorption of 12.2 kJ mol−1. These findings are corroborated by temperature-programmed desorption spectroscopy and van der Waals-corrected density functional theory calculations. In addition to its exceptional hydrogen capacity, Ni2(dondc) exhibits robust structural stability and long-term durability, positioning it as a promising candidate for near-ambient-temperature hydrogen storage applications.

Efficient Ni/Y2O3 catalyst prepared by sol-gel self-combustion method for ammonia decomposition to hydrogen

Ammonia has sparked a lot of interest as a promising hydrogen carrier for the development of renewable energy and as a workable method to produce COx-free hydrogen for fuel cells through its on-site decomposition. The catalysts, composed of nickel as an active metal supported on the Y2O3, were synthesized by the sol-gel self-combustion method conveniently, in which the active metals are uniformly dispersed. 700–1.25Ni1Y1Oα exhibits the best catalytic activity and has the most active metal dispersion (6.15 %). The ammonia conversion can reach 96 % at 550 °C and 12000 ml·gcat−1·h−1 gas hourly space velocities (GHSVs) as well as 100 % at 600 °C and the same GHSVs. Temperature-programmed reduction, temperature-programmed desorption, and X-ray photoelectron spectroscopy were used to characterize the catalysts. It was found that 700–1.25Ni1Y1Oα has the best capacity for hydrogen desorption resulting in weakening the inhibitory effect of hydrogen to the reaction and enhancing the reactivity of the catalyst. The electron transfer from Y in Y–O–Ni structure increases gradually as the Ni to Y ratio becomes appropriate, enhancing the alkalinity of the catalyst and electron density around the Ni, which is beneficial to NH3 decomposition.

Inhibition effect of three types of biochar on volatile organic compounds from asphalt: Revealing chemical adsorption as the primary mechanism

For advancing sustainable and eco-friendly road materials, addressing the emissions of volatile organic compounds (VOCs) from asphalt binders is paramount. As an environment-friendly adsorbent, biochar is highly promising for mitigating such VOCs emissions. Herein, the feasibility and mechanism of using biochar to control VOCs emissions from asphalt were investigated. Biochar was derived from rice husk, straw and coffee grounds. The VOCs composition was analysed using thermal desorption–gas chromatography–mass spectrometry. Differential scanning calorimetry was employed to simulate asphalt VOCs release, while temperature-programmed desorption spectroscopy was employed to investigate biochar inhibition. Rice husk–derived biochar exhibited the highest inhibition effect on asphalt VOCs. The inhibitory effects of the three biochar samples were weakened with increasing number of carbon atoms in organic compounds, with less ideal inhibition efficiency for aromatic compounds. Chemical adsorption was the primary mechanism for the inhibition of VOCs emissions by biochar at high temperatures.

Optimum relative humidity enhances CO2 uptake in diamine-appended M2(dobpdc)

Diamine-appended M2(dobpdc) metal–organic frameworks (MOFs) are a promising class of CO2 adsorbents, but the impact of relative humidity (RH) on their adsorption performance has yet to be carefully studied. We evaluated the CO2 uptake of (2-ampd)2M2(dobpdc) at varying relative humidities and associated water loadings using gravimetric and breakthrough adsorption methods. A significant enhancement in uptake is observed between 20 and 40 % RH, with an optimum of 30 % RH, at which a maximum CO2 uptake of 5.7 ± 0.2 mmol/g is achieved at 0.044 atm of CO2. These uptakes – which are above 1 CO2:diamine – suggest that humidity promotes an additional sorption mechanism beyond the well-known cooperative insertion between the metal and diamine. Temperature-programmed desorption and IR spectroscopy also indicated a second adsorption site accounting for the additional uptake, hypothesized to be carbamic acid pairs on the free amine within the MOF channel. Further increasing the humidity to 50 % RH resulted in a dramatic loss of capacity due to water-filled pores at these high humidity conditions. These results reveal the potential for a mixed mechanism in (2-ampd)2M2(dobpdc) promoted by humidity and highlight an optimum humidity range that will maximize the MOF’s utilization in CO2 capture applications.

Pt-Doped Lanthanum Ferrites as Versatile Electrode Material for Solid Oxide Cells

La0.6Sr0.4Fe0.8Co0.2O3-δ (LSCF) alone or mixed with doped ceria represents the reference air electrode material for IT-SOFC/SOEC, thanks to its intrinsic MIEC nature and unrivaled catalytic activity towards oxygen exchange reactions. Nevertheless, a steep growth in cobalt demand for automotive (EVs) and storage applications is expected in the next decades, and ethical issues related to cobalt mining in politically unstable countries endanger cobalt supply chain [1]. Noble metal doping to a low extent ( ≤ 5% mol) has drawn attention as a valid strategy to provide the parent oxide structure with high catalytic activity [2][3]. Such amounts of platinum-group-metals (PGM) could be profitably harvested from secondary sources, such as spent automotive three-way catalysts (TWCs) [4], rendering their supply less dependent from localized low-grade ores. In particular, due to the tendency of PGM to be easily reduced to the metallic state, PGM-doped perovskites have found application mainly as fuel electrode materials. Noble metal exsolution endows the parent perovskite with finely dispersed nanoparticles firmly anchored to the oxide substrate, that display high catalytic activity and stability [5].Here, platinum-doping on strontium-substituted lanthanum ferrites is explored as an innovative strategy to enhance the parent perovskite catalytic activity both in reducing and oxidizing environment. The ultimate goal is the design of a multi-functional electrode for Reversible Solid Oxide Cells (r-SOCs). La0.6Sr0.4Fe1-xPtxO3-δ, X = 0.005, 0.01, 0.05 (LSFPtX) stoichiometries were successfully synthesized and characterized by means of X-ray Powder Diffraction (XPRD) (Fig. 1), thermogravimetric analysis (TG), oxygen temperature-programmed desorption (O2-TPD) and X-ray photoelectron spectroscopy (XPS). LSFPtX were tested in symmetric cells to evaluate their activity as air electrode materials in terms of polarization resistance vs. temperature and vs. pO2. The rate-limiting steps of oxygen exchange reactions were investigated by means of electrochemical impedance spectroscopy (EIS) fitting experimental data with equivalent circuit (EC) modelling and distribution of relaxation times (DRT). Results were compared both to the undoped (LSF) and to a commercially available state-of-art 20 mol% Co-substituted LSCF. LSFPtX structural evolution is evaluated at different pO2 and in several SOCs operational environments (5%H2/Ar, 100% CO2 and 50% CO2 : 50% CO). B-site exsolution was studied by means of temperature-programmed reduction (H2-TPR) and scanning electron microscopy (FE-SEM) to assess their applicability as fuel electrode materials as well. Finally, LSGM-based symmetric cells were tested as SOFC and CO2-SOEC, evaluating the operational reversibility and the long-term stability.[1] IEA, Total Cobalt Demand by Sector and Scenario, October 2022, pp. 2020–2040.[2] Marcucci, A., Zurlo, F., Sora, I. N., Placidi, E., Casciardi, S., Licoccia, S., & Di Bartolomeo, E. (2019). A redox stable Pd-doped perovskite for SOFC applications. Journal of Materials Chemistry A, 7(10), 5344-5352.[3] Marasi, M., Duranti, L., Luisetto, I., Fabbri, E., Licoccia, S., & Di Bartolomeo, E. (2023). Ru-doped lanthanum ferrite as a stable and versatile electrode for reversible symmetric solid oxide cells (r-SSOCs). Journal of Power Sources, 555, 232399.[4] Karim, S., & Ting, Y. P. (2021). Recycling pathways for platinum group metals from spent automotive catalyst: A review on conventional approaches and bio-processes. Resources, Conservation and Recycling, 170, 105588.[5] Kothari, M., Jeon, Y., Miller, D. N., Pascui, A. E., Kilmartin, J., Wails, D., ... & Irvine, J. T. (2021). Platinum incorporation into titanate perovskites to deliver emergent active and stable platinum nanoparticles. Nature Chemistry, 13(7), 677-682. Figure 1

Robust Pd/Al2O3 bifunctional catalyst for single reactor tandem synthesis of furan and tetrahydrofuran derivatives from furfural

In this study, we report a reusable catalytic system based on a bifunctional Pd/Al2O3 spheres to conduct the single-reactor tandem aldol condensation/crotonization reaction between furfural and methylisobutyl ketone, followed by hydrogenation, both in batch and continuous mode. In batch mode, the process achieved an overall 86 % yield of 1-(tetrahydrofuran-2-yl)-5-methylhexan-3-one at 180 °C after 9 h at (5.2 wt% furfural concentration). The reaction rate for the aldol condensation/crotonization step decreased at higher FF concentration, suggesting the inhibition of Lewis acid centers due to adsorbed FF as inferred from kinetic modeling. In continuous mode, the catalyst was operated in a dual-type fixed bed reactor and reached 55 % steady-state conversion and 60 % and 35 % selectivity to 1-(furan-2-yl)-5-methylhexan-3-one and (E)-1-(furan-2-yl)-5-methylhex-1-en-3-one, respectively, after 12 h operation at 170 °C and a weight-hourly space velocity of 0.50 h−1 at high furfural concentration (18 wt%). NH3/CO2 temperature-programmed desorption and FT-IR spectroscopy implemented with adsorbed pyridine, NH3 and CO2 were used to assess the nature, strength, density and stability of the acid and basic sites.

Improved photocatalytic H2O2 production of boron doped g-C3N4 by controllably co-modifying nanosized PDI and Ag

Herein, boron-doped g-C3N4 (BCN) is first modified with perylene diimide (PDI) nanosheets driven by the π−π interactions, and subsequently decorated with nanosized Ag through the photodeposition method. The optimal PDI/BCN-Ag photocatalyst achieves a H2O2 production rate of 143 μmol g−1 h−1 without any sacrificial agents under visible light irradiation, which is about13-fold improvement compared with pristine g-C3N4. The boosted photoactivity is mainly ascribe to the enhanced charge separation due to the cascade S-scheme charge transfer between the coupled PDI and BCN, and the promoted oxygen activation from the introduced nanosized Ag by means of the time-resolved surface photovoltage responses and fluorescence spectra, kelvin probe measurement analyses, O2 temperature-programmed desorption and electron paramagnetic resonance spectroscopy. Notably, there is a dual channel for H2O2 production on PDI/BCN-Ag. The two-electron oxygen reduction dominated by the produced •O2− radicals occurs on the Ag nanoparticles, whereas the two-electron water oxidation occurs on the PDI.

Trimetallic Oxide Foam as an Efficient Catalyst for Fixation of CO2 into Oxazolidinone: An Experimental and Theoretical Approach

The excess anthropogenic CO2 depletion via the catalytic approach to produce valuable chemicals is an industrially challenging, demanding, and encouraging strategy for CO2 fixation. Herein, we demonstrate a selective one-pot strategy for CO2 fixation into "oxazolidinone" by employing stable porous trimetallic oxide foam (PTOF) as a new catalyst. The PTOF catalyst was synthesized by a solution combustion method using transition metals Cu, Co, and Ni and systematically characterized by X-ray diffraction (XRD), thermogravimetric analysis (TGA), field emission scanning electron microscopy (FE-SEM), high-resolution transmission electron microscopy (HR-TEM), N2 sorption, temperature-programmed desorption (TPD), and X-ray photoelectron spectroscopy (XPS) analysis. Due to the distinctive synthesis method and unique combination of metal oxides and their percentage, the PTOF catalyst displayed highly interconnected porous channels along with uniformly distributed active sites on its surface. Well ahead, the PTOF catalyst was screened for the fixation of CO2 into oxazolidinone. The screened and optimized reaction parameters revealed that the PTOF catalyst showed highly efficient and selective activity with 100% conversion of aniline along with 96% selectivity and yield toward the oxazolidinone product at mild and solvent-free reaction conditions. The superiority of the catalytic performance could be due to the presence of surface active sites and acid-base cooperative synergistic properties of the mixed metal oxides. A doubly synergistic plausible reaction mechanism was proposed for the oxazolidinone synthesis experimentally with the support of DFT calculations along with bond lengths, bond angles, and binding energies. In addition, stepwise intermediate formations with the free energy profile were also proposed. Also, the PTOF catalyst displayed good tolerance toward substituted aromatic amines and terminal epoxides for the fixation of CO2 into oxazolidinones. Very interestingly, the PTOF catalyst could be significantly reused for up to 15 consecutive cycles with stable activity and retention in physicochemical properties.

Interaction of Atomic Deuterium with Rutile TiO2(011)-(2×1)

Inspired by the significance of hydrogen–solid interaction in hydrogen energy and catalysis, adsorption, diffusion, and desorption behaviors of deuterium atoms in rutile TiO2(011) have been investigated by temperature-programmed desorption (TPD) and ultraviolet photoelectron spectroscopy (UPS). Upon exposure, a small portion of D atoms adsorb at surface oxygen sites, resulting in the band gap states at 1.35 eV below the Fermi level and desorbing as water at ∼400 K. Most of the D atoms will diffuse into the bulk due to the relatively low activation barrier and the huge capacity of the solid material. These bulk D species desorb as D2/HD between 500 and 800 K. While the desorbing D2O from surface hydroxyls saturates at ∼0.10 monolayer (ML), the yielding D2 is about 96 ML (equivalent coverage) at the largest atomic D exposure of 4.54 langmuir and no saturation trend has been observed in the present work. Detailed analysis indicates the bulk D will diffuse back to the surface and recombine as D2 at elevated temperatures. The differences between the behavior of H(D) in rutile TiO2(110) and TiO2(011) have been discussed by considering the presence of additional bridging oxygen atoms between the in-plane and topmost ones on the latter surface. The striking finding that most surface D atoms diffuse into the bulk of rutile TiO2(011) will not only broaden our understanding of the interaction of H/D with the prototypical metal oxide material but also provide clues to investigate the mechanism of H/D involving reactions over TiO2 catalysts, for example, hydrogen evolution and hydrogenation.

Stability of Graphene/Intercalated Oxygen/Ru(0001) as Studied by Thermal Desorption of CO and CO2 Molecules

Formation of graphene on Ru(0001) by exposure to ethylene and subsequent annealing has been studied by low-energy electron diffraction, X-ray photoelectron spectroscopy, and ultraviolet photoelectron spectroscopy. The stability of graphene/intercalated oxygen/Ru(0001) has been investigated by temperature programmed desorption spectroscopy. Desorption of CO and CO2 was observed upon heating the samples to temperatures above 700 K. It was found that the graphene layer was partly intact after the desorption run and that the intercalated oxygen was removed. It was concluded that the oxygen-intercalated graphene layer was stable up to temperatures of about 700 K.

Chemistry of zipping reactions in mesoporous carbon consisting of minimally stacked graphene layers.

The structural evolution of highly mesoporous templated carbons is examined from temperatures of 1173 to 2873 K to elucidate the optimal conditions for facilitating graphene-zipping reactions whilst minimizing graphene stacking processes. Mesoporous carbons comprising a few-layer graphene wall display excellent thermal stability up to 2073 K coupled with a nanoporous structure and three-dimensional framework. Nevertheless, advanced temperature-programmed desorption (TPD), X-ray diffraction, and Raman spectroscopy show graphene-zipping reactions occur at temperatures between 1173 and 1873 K. TPD analysis estimates zipping reactions lead to a 1100 fold increase in the average graphene-domain, affording the structure a superior chemical stability, electrochemical stability, and electrical conductivity, while increasing the bulk modulus of the framework. At above 2073 K, the carbon framework shows a loss of porosity due to the development of graphene-stacking structures. Thus, a temperature range between 1873 and 2073 K is preferable to balance the developed graphene domain size and high porosity. Utilizing a neutron pair distribution function and soft X-ray emission spectra, we prove that these highly mesoporous carbons already consist of a well-developed sp2-carbon network, and the property evolution is governed by the changes in the edge sites and stacked structures.

Investigation of the synergetic regulation of O2/Ar preheating treatment and sodium salt addition on semichar combustion characteristics

Using Raman spectroscopy, temperature-programmed desorption (TPD) and laser-induced breakdown spectroscopy (LIBS), the relationship between microstructural characteristics and molecular emissions was determined. It can be concluded that the enhancement of C2 and CN emissions was related to the generation of small aromatic rings and C(O) groups. Compared with the Ar preheating treatment, the presence of additional amount of O2 and sodium salt accelerated the dissociation of the large aromatic ring skeleton, leading to the significant enhancement of small aromatic rings, C(O) and CONa groups. Subsequently, the combustion performance of preheated semichar was investigated by the TG-DTG method. The experimental results demonstrated that pretreatment under oxidizing atmospheres (without and with sodium salt addition) enhanced the comprehensive combustion index (S) and the combustion stability (Rw) of semichars. The corresponding combustion activation energy (E) was weakened. Furthermore, the DFT method was used to analyse the combustion behaviours of semichars. This result demonstrated that preheating treatment (with or without sodium participation) altered the distribution of the Hirshfeld atomic charge (ADCH) of preheated samples, and the combustion essence of semichar was the fracture and recombination of aromatic clusters. For the semichar preheated in the O2/Ar atmosphere, the energy gap of the most optimized pathway was 436.26 kJ/mol. When sodium participated in the oxidizing pretreatment, the energy gap of the most optimized pathway was 413.80 kJ/mol. The positive effect of sodium on the combustion performance of semichar was identified, which was in good agreement with the experimental results.

Chemisorption of CO2 on Nitrogen-Doped Graphitic Carbons.

The adsorption of CO2 on nitrogen-doped graphitic carbon materials, such as graphene nanosheet (GNS) powder and highly oriented pyrolytic graphite (HOPG), was comparatively studied using temperature-programmed desorption (TPD) and X-ray photoelectron spectroscopy (XPS). Desorption of CO2 was observed at approximately 380 K for both pyridinic-nitrogen (pyri-N)-doped GNS and pyri-N-doped HOPG samples in the TPD experiments, whereas no CO2 desorption was observed for graphitic nitrogen-doped HOPG. This indicated that only pyri-N species create identical CO2 adsorption sites on any graphitic carbon surface. The adsorption energies of CO2 on pyri-N-doped carbons were estimated between 101 and 108 kJ mol-1, indicating that chemisorption, rather than physisorption, took place. The CO2 adsorption/desorption process was reproducible in repeated measurements, and no CO2 dissociation occurred during the process, suggesting that it is a promising CO2 capturing material. The O 1s peak of the adsorbed CO2 clearly appeared at 531.5-532 eV in the XPS measurements. The N 1s peak of pyri-N did not change with CO2 adsorption, indicating that CO2 is not directly bound to pyri-N but is adsorbed on a carbon atom near the pyridinic nitrogen via the nonbonding pz orbital of the carbon atom.

On thermal stability and decomposition mechanisms of aromatic diamines employed as links in novel Pt nanoparticle network catalysts

The thermal stability of microporous networks of Pt nanoparticles interlinked by p-Phenylenediamine (PDA) was investigated by temperature-programmed desorption spectroscopy (TPD) and transmission electron microscopy (TEM). The detection of aniline, benzene, and NH3 as major desorbing fragments in TPD revealed cleavage of the C-N bonds in PDA as a major route of thermally induced decomposition, probably via hydrogenolysis assisted by dehydrogenation reactions of PDA running alongside. Varying the Pt:PDA ratio in the networks demonstrated that the Pt nanoparticles catalytically promote the decomposition of their PDA links. A quantitative analysis of the TPD spectra indicated that the thermal stability of PDA strongly correlates with the number of bonds (0, 1 or 2) formed by the amino groups of an individual PDA molecule with Pt. Only the most stable PDA species appears to be of relevance for the structural stability of the nanoparticle network, as heating experiments with in situ TEM showed. The results have strong implications for the application of PDA-linked Pt nanoparticles as heterogeneous catalysts in hydrogen gas microsensors where the choice of operating temperature has to balance maximization of signal-to-noise ratio and maintenance of structural stability. An anealing step up to 450–500 K after synthesis of the catalyst is suggested in order to optimize its catalytic activity by removing PDA species that are not essential for structural stabilty.

Cu/ACF adsorbent modified by non-thermal plasma for simultaneous adsorption–oxidation of H2S and PH3

Non-thermal plasma (NTP) surface modification technology is a new method to control the surface properties of materials, which has been widely used in the field of environmental protection because of its short action time, simple process and no pollution. In this study, Cu/ACF (activated carbon fiber loaded with copper) adsorbent was modified with NTP to remove H2S and PH3 simultaneously under low temperature and micro-oxygen condition. Meanwhile, the effects of different modified atmosphere (air, N2 and NH3), specific energy input (0–13 J/mL) and modification time (0–30 min) on the removal of H2S and PH3 were investigated. Performance test results indicated that under the same reaction conditions, the adsorbent modified by NH3 plasma with 5 J/mL for 10 min had the best removal effect on H2S and PH3. CO2 temperature-programmed desorption and X-ray photoelectron spectroscopy (XPS) analyzes showed that NH3 plasma modification could introduce amino functional groups on the surface of the adsorbent, and increase the types and number of alkaline sites on the surface. Brunauer-Emmett-Teller and scanning electron microscopy showed that NH3 plasma modification did not significantly change the pore size structure of the adsorbent, but more active components were evenly exposed to the surface, thus improving the adsorption performance. In addition, X-ray diffraction and XPS analysis indicated that the consumption of active components (Cu and Cu2O) and the accumulation of sulfate and phosphate on the surface and inner pores of the adsorbent are the main reasons for the deactivation of the adsorbent.

One pot sol-gel synthesis of Pt−Ni/TiO2 with high CO2 methanation catalytic activity at low temperature

In this work, 2 wt%Pt/TiO2, 20 wt%Ni/TiO2 monometallic catalysts and xwt%Pt−20 wt%Ni/TiO2 (x = 1, 2 and 4 wt%) bimetallic catalysts were synthesized by one-pot sol-gel method for CO2 methanation reaction. All bimetallic catalysts revealed higher CO2 conversion than both monometallic catalysts. The 2 wt%Pt−20 wt%Ni/TiO2 catalyst exhibited the highest percentage of CO2 conversion at low reaction temperature, with almost 100% CH4 selectivity and high stability during 72 h time on stream. The effect of Pt co-doped with Ni to bimetallic formed on the catalyst properties was studied using several techniques, including X-ray diffraction, N2 adsorption-desorption, Raman spectroscopy, transmission electron microscopy, field emission scanning electron microscopy, H2 temperature-programmed desorption, H2 temperature-programmed reduction, CO2 temperature-programmed desorption and X-ray absorption spectroscopy (both ex-situ and in-situ experiments). The results showed that Pt was dispersed on the catalyst surface in the form of platinum oxide, while Ni was both incorporated into the TiO2 lattice with the excess amount from saturated level being dispersed on the catalyst surface. The results from XAS evidenced that some electrons movement from Ni to Pt occurred. This electronic property changing can tune the interaction between Ni and TiO2 support with appropriate strength and then resulting in higher reducibility of the catalyst and higher dispersion of Ni species. Furthermore, the electron-rich Pt site on the catalyst surface favored to adsorb CO from CO2 dissociation and further activated adsorbed CO to interact with nearby hydrogen atoms to form CH4 leading to high CO2 methanation activity at low temperature.

Contribution of Na/K Doping to the Activity and Mechanism of Low-Temperature COS Hydrolysis over TiO2-Al2O3 Based Catalyst in Blast Furnace Gas

As an organic sulfur pollutant generated in blast furnace gas, carbonyl sulfide (COS) has attracted more attention due to its negative effects on the environment and economy. The TiO2-Al2O3 composite metal oxide (Ti0.5Al) with uniformly dispersed particles was prepared by the co-precipitation method. And on this basis, a series of Na/K-doped catalysts were prepared separately. The activity evaluation results showed that the introduction of Na/K significantly improved the low-temperature COS hydrolysis activity, which exhibited a COS conversion of 98% and H2S yield of 95% at 75 °C with 24,000 h–1. And K showed a better promoting effect than Na. Brunauer–Emmett–Teller (BET) results revealed the increased mesopore proportion of Na/K-modified catalysts. X-ray diffraction (XRD) and scanning electron microscopy (SEM) showed that Na and K formed prismatic and nanorod-like structures, respectively. More weakly basic sites with enhanced intensity and decreased Oads/Olat content contributed to the excellent catalytic activity, as certified by the results of CO2 temperature-programmed desorption (CO2-TPD) and X-ray photoelectron spectroscopy (XPS). It was also proposed that the decrease of weakly basic sites ultimately deactivated catalyst activity. In situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) showed that the introduction of Na/K enhanced the dissociation of H2O, and the generated abundant hydroxyl groups promoted the adsorption of COS and formed surface transition species, such as HSCO2– and HCO3–.

Energetic characteristics of hydrogenated amorphous silicon nanoparticles

• Plasma-synthesized amorphous Si NPs ( a -nSi) incorporate abundant hydrogen. • The reactivity of a -nSi/KClO 4 increases by a factor of six compared with nAl. • The energetic performance of nSi is correlated with its hydrogen content. • In situ release of hydrogen from hydrides enhances the reactivity. In this work, we utilize a low-temperature non-equilibrium plasma to nucleate and grow sub-10 nm Si particles with varying degrees of crystallinity by tuning the level of power coupled into plasma discharge. Temperature-programmed desorption spectroscopy shows that as-prepared amorphous Si nanoparticles ( a -nSi) incorporate more hydrogen than crystalline Si nanoparticles ( c -nSi). Further, hydrogen is incorporated in the material in the form of higher silicon hydrides with a lower desorption temperature. Combustion cell measurements show that when formulated with KClO 4 , a -nSi outperforms its crystalline counterpart with respect to pressure output. The pressurization rate of a -nSi/KClO 4 composite increases by a factor of six compared with nAl to 0.66 MPa·μs −1 . Evidence of hydrogen release (∼730 K) from Temperature-jump time-of-flight mass spectrometry (T-Jump TOFMS) of a -nSi/KClO 4 suggests the creation of Si dangling bonds prior to ignition (∼820 K), which then react exothermically with oxygen liberated from KClO 4 , leading to ignition. Explosive reaction of H 2 /O 2 mixture likely contributes to the rapid pressure rise. The enhanced energetic performance of hydrogenated a -nSi compared to its crystalline counterpart suggests that incorporation of hydrogen is a promising strategy for improving the performance of nanoenergetic materials.

Acidic property of YNU-5 zeolite influenced by its unique micropore system

YNU-5 zeolite has the YFI -type framework with a 12-12-8-ring system (2-dimensional 12-oxygen membered ring pores 3-dimensionally connected by twin 8-ring channels), and isolated 8-ring channels separated from the system by a thin (mono-atomic silicate) wall. In this study, the acidic property of YNU-5 zeolite was analyzed mainly by means of the ammonia IRMS-TPD (infrared/mass spectroscopy temperature-programmed desorption) method. In addition, the accessibility of acid sites was evaluated through adsorption of pyridine. The number of Brønsted acid sites approximately agreed with the number of Al atoms, and the amount of Lewis acid sites was negligible, indicating that most acid sites have the nature of bridging Si(OH)Al group in the YFI framework. Most of the Brønsted acidic OH groups on the YNU-5 zeolites (including the dealuminated samples) reacted with pyridine vapor at 343 K to form pyridinium cations, indicating that the Brønsted acid sites are highly accessible through the 12-12-8-ring system. Enthalpy of ammonia desorption from the Brønsted acid site, which can be an index of acid strength or reactivity of the acid site with a basic reactant, was in the following order: FAU < MOR (12-ring) ≈ *BEA < MFI < MWW ≈ YFI < MOR (8-ring), indicating the markedly large ammonia desorption enthalpy on the YNU-5 zeolite compared to the other 12-ring zeolites. The DFT calculations suggest that the Brønsted acidic protons with especially high ammonia desorption enthalpy are located in the isolated 8-ring but accessible from the 12-12-8-ring system side. In addition, dealumination at a high temperature under the reflux conditions with nitric acid resulted in the preferential removal of Brønsted acid sites with low ammonia desorption enthalpy, probably in the 12-12-8-ring system. The presence of reactive Brønsted acid sites in the isolated 8-ring, accessibility to them from the 12-12-8-ring system, and preferential removal of the Brønsted acid sites from the 12-12-8-ring system are reasonably consistent with the previously reported catalytic properties for dimethyl ether-to-olefin reaction. • Enthalpy of ammonia desorption (Δ H ) from the Brønsted acid site on the YNU-5 zeolite was high. • The Brønsted acidic protons with high Δ H were located in the isolated 8-ring but accessible from the 12-12-8-ring system. • Dealumination in the reflux conditions of nitric acid preferential proceeded in the 12-12-8-ring system.

Investigation of the modes of NO adsorption in Pd/H-CHA

This study investigates NO adsorption on Pd-exchanged chabazite (Pd/H-CHA), a promising passive NOx adsorber (PNA) for capturing cold-start NOx emissions of gasoline- and diesel-powered vehicles. Temperature-programed desorption (TPD) and IR spectroscopy are combined with theoretical calculations to elucidate how and where NO is stored, and how water and O2 affect this process. NO adsorption on Pd/H-CHA produces two TPD features, around 423 and 753 K, and IR bands centered at 1860 and 1810 cm−1. Calculated NO stretching frequencies and maximum-desorption temperatures reveal that Pd2+ and Pd+ sites are responsible for these low- and high-temperature features, respectively, and that while the IR feature at 1810 cm−1 is due to NO adsorption on Pd+, the 1860 cm−1 feature contains contributions from both weakly-bound NO on Pd2+ and more strongly bound NO on Pd+, consistent with experimentally observed effects of water and O2.