Applications of Adsorption Microcalorimetry to the Study of Heterogeneous Catalysis

Adsorption of gas molecules on group III atoms adsorbed g-C3N4: A first-principles study

We have investigated the adsorption of CO, NO, CO2, and NO2 gas molecules on ultra-thin graphene nanoribbons (GNRs) using density functional theory-based calculations. In both armchair and zigzag GNR, the gas molecules stabilize at the center of hexagonal ring and interact weakly with GNR with adsorption energy in the range of −0.06 to −0.56 eV. The change in the electron density of states near fermi level on adsorption of gas molecules show that pristine GNR is more sensitive for NO2 in comparison to CO, NO and CO2. When dopant (B & N) and vacancy defect are introduced in the GNR surface, the adsorption of gas molecules is enhanced with higher interaction energy in the range −0.19 to −0.87 eV. The electronic properties of GNR shows strong dependence with width upto 5 layers and shows no change in the electronic properties with further increase in the width. The adsorption of gas molecules changes Electronic density of states (DOS) of GNRs near fermi level due to charge transfer and rearrangement. CO, CO2, and NO2 molecules behave as charge acceptor whereas NO molecule act as a charge donor. The result can be explained based on number of size dependent electronic properties of GNRs and nature of dopants/defects.

Adsorption of O3, SO2 and SO3 gas molecules on MoS2 monolayers: A computational investigation

In this thesis a study is focused on the synthesis of organic compounds of interest in Fine Chemistry and biomass derivatives by design of more sustainable chemical processes and the use of heterogeneous catalysts with the optimal properties for each reaction.\nIn the first approach, it has been carried out the synthesis of nitriles, compounds of great application in the chemical and pharmaceutical industry, by the dehydration of aldoximes in the presence of different heterogeneous catalysts with both acidic and basic properties. Catalytic studies showed that the best results in terms of nitrile yield and selectivity are obtained with catalysts having Lewis acid centers. Among them, the iron MOFs (MIL-100 (Fe) and Fe (BTC)) proved to be the most suitable catalysts for this reaction obtaining excellent yields and selectivity towards nitriles. By means of a post synthesis treatment with ammonium fluoride it was possible to increase the catalytic activity of MIL-100 (Fe) increasing its BET area and pore volume. Studies using IR spectroscopy and XPS analysis led to the conclusion that the catalytic activity of MIL-100 (Fe) is related to the Fe species of the crystalline lattice. It has been shown that MIL-100 (Fe) -NH4F is stable and reusable in several consecutive reaction cycles without loss of activity and has been successfully applied to the synthesis of a wide variety of nitriles.\nOn the other hand, the synthesis of nitriles from aldoximes was carried out in the presence of several metal oxides, being cerium oxide the most active catalyst. The acid-base properties of the metal oxides were studied by the adsorption of probe molecules on their surface analyzed by IR spectroscopy. Thus, a relationship between the acid-base properties of the oxides with their catalytic activity was established, being the oxides with the strongest basic centers such as CeO2 and MgO the most active catalysts. Based on the IR studies of the aldoxime dehydration reaction on the surface of MgO and CeO2 in situ, a mechanism of reaction was proposed. Excellent yields were obtained for aromatic, aliphatic and cyclic nitriles using cerium oxide as the catalyst. In addition, CeO2 proved to be a stable and reusable catalyst being possible to be reused during four consecutive cycles without loss in its catalytic activity. The study was expanded to obtain different amides and esters with pharmacological properties from aldoximes by one-pot processes using the nanocrystalline cerium oxide as a catalyst.\nFinally, the work is focused on obtaining products derived from biomass, specifically on the synthesis of DFF and furylidenpropanenitrile derivatives with potential application as monomers. The DFF was obtained by carrying out the oxidation of 5-HMF in the presence of several MOFs as heterogeneous catalysts. It was shown that using the MIL-100 (Fe)-NH4F/TEMPO/NaNO2 as catalyst system for the oxidation of 5-HMF it is possible to obtain 100% yield and 100 % selectivity to DFF. In addition, this catalytic system was used for the oxidation of different primary and secondary alcohols obtaining good yields to the corresponding carbonyl compounds. Finally, in a second step the synthesis of furylidenepropanenitrile derivatives was carried out by Knoevenagel condensation between previously obtained DFF and active methylene compounds (malononitrile and ethyl cyanoacetate) obtaining excellent yields to the desired products.\n¿

Adsorption of gas molecules on Ga-doped graphene and effect of applied electric field: A DFT study

Using first-principles calculations, the effects of residual gas molecules (H2O, CO, CO2, H2 and N2) adsorption on the photoelectric properties of pristine and Zn-doped GaAs nanowire surfaces are investigated. Total energy calculations show that p-type doping surface is beneficial to reduce the damage of residual gases to cathodes and improve the stability of GaAs nanowire photocathodes. After adsorption of gas molecules, the electrons are transferred from surface to adsorbates, leading to a dipole moment pointing from surface to residual gas molecules, which obstructs the escape of electrons and increases the work function of photocathodes. Through Zn doping, the charge transfer between gas molecules and nanowire surface is reduced and the force of dipole moment induced by gas molecules is weakened. Besides, the conduction energy bands shift toward higher energy region and the band gap increased after adsorption of residual gas molecules. Moreover, residual gas adsorption will weaken the absorption characteristic of GaAs nanowire photocathodes.

Adsorption behavior and sensing properties of toxic gas molecules onto PtnBe (n = 5, 7, 10) clusters: A DFT benchmark study

Adsorption of polar probe molecules on plasma-oxidised high-strength carbon fibres

Adsorption of toxic gas molecules on the pre-oxidized Cu2Si nanosheet – A DFT study

Adsorption of gas molecules on Cu impurities embedded monolayer MoS2: A first- principles study

Characterisation of clays and aluminium pillared clays by adsorption of probe molecules

An environmentally responsible and sustainable replacement for finite fossil fuels is biodiesel. Because of its amazing qualities, biodiesel is becoming more and more popular as a renewable fuel around the globe. The many approaches, feedstocks, catalysts, comparison standards, reaction kinetics, final product analysis, and final product characterization of biodiesel are covered in this review article. Researchers have used a variety of techniques to produce biodiesel throughout history, with transesterification emerging as the most effective approach in more recent times. Numerous studies on biodiesel feedstock and catalysts to produce high biodiesel yields have been published; nevertheless, it should be highlighted that the type of feedstock must be considered while choosing a catalyst. The review paper highlights the significance of several parameters that are crucial to the manufacture of biodiesel, without which achieving a high yield would be challenging. The literature has also discussed the limitations and advantages of different catalysts, and scientists are currently working to identify the ideal catalyst within certain optimal parameters for the manufacture of biodiesel. Homogeneous reaction‐based biodiesel synthesis has a number of drawbacks, though, such as water content, a laborious purification procedure, and a low tolerance for free fatty acids. To address these issues, scientists have started investigating heterogeneous reactions involving solid catalysts. A large pore network, a moderate‐to‐high density of strong acid sites, a hydrophobic surface, and the ability to control surface hydrophobicity to avoid deactivation are all desirable characteristics of an ideal solid catalyst. Ion exchange resins, sulfated oxides, heterogeneous base catalysts, boron group‐based heterogeneous catalysts, alkaline earth metal oxides, mixed metal oxides, alkali metal oxides, heterogeneous catalysts derived from waste materials, and different approaches to biodiesel synthesis that employ enzymes, carbon‐based heterogeneous catalysts, and ionic liquids as catalysts are among the categories of catalysts that can be used in the production of biodiesel. The finest benchmarks to compare the quality of biodiesel with European and American Society for Testing Material standards. For detailed characterization of the finished product, gas chromatography and nuclear magnetic resonance are the most effective methods.

DFT outcome for comparative analysis of Be12O12, Mg12O12 and Ca12O12 nanocages toward sensing of N2O, NO2, NO, H2S, SO2 and SO3 gases

Recent reports have raised exciting prospects for the use of C3N monolayers exhibiting excellent adsorptive properties in nanodevice applications. In this study, we carried out first-principle calculations to investigate the adsorption of NO2, NO, CO, HCN, NH3, CO2, H2, N2, CH4, H2O, O2, and N2O gas molecules on a C3N monolayer as well as its potential applications in gas sensor devices. Our results reveal that the chemisorption of NO2 can significantly influence the electronic properties of the C3N monolayer (e.g., changing semiconducting behavior to conducting behavior). In contrast, physisorption of the other gas molecules had little effect on the electronic properties of the C3N monolayer. These results suggest that the C3N monolayer is much more sensitive and selective to NO2 than to the other gases. The recovery time of NO2 at T = 300 K is only 0.62 s. Moreover, the optical properties of the C3N monolayer can be modified as a result of the adsorption of different molecules, especially the NO2 molecule. Thus, the C3N monolayer is a promising and desirable candidate for use as a suitable material in gas sensors for NO2 detection.

This work reports the fabrication of porous mixed metal oxide (MMO)–TiO2 one-dimensional photonic crystals (1DPCs), which can be used as a colorimetric sensor for the detection and measurement of volatile organic compounds (VOCs) and relative humidity (RH). The 1DPCs were prepared via the alternate deposition of titania and layered double hydroxide (LDH) by the spin-coating technique followed by calcination (which induces the phase transformation of LDH to MMO material). A photonic stop band (PSB) of MMO–TiO2 1DPCs was obtained, which can be tuned throughout the whole visible light region by changing the thickness of either of the composing slabs, as a result of the sufficiently high refractive index contrast between TiO2 and MMO. The 1DPC film as a colorimetric sensor shows significant color variation towards VOCs or RH, due to the change of refractive index induced by the adsorption of volatile gas or water molecule in the mesopores of the MMO–TiO2 structure. In addition, the sensor displays high sensitivity, good stability and reproducibility. Therefore, this work provides a feasible method for the fabrication of 1DPCs based on porous MMO–TiO2 films, which have potential applications as portable, recyclable and visually readable colorimetric sensors.