Study of the Temperature-Programmed Desorption of Carbon Dioxide (CO2) on Zeolites X Modified with Bivalent Cations

Study of physisorbed and chemisorbed carbon dioxide (CO2) species was carried out on the NaX zeolite modified by cationic exchanges with bivalent cations (Ca2+ and Ba2+) by temperature-programmed desorption of CO2 (CO2-TPD). Others results were obtained by infrared to complete the study. The results of this research showed, in the physisorption region (213 - 473 K), that the cationic exchanges on NaX zeolite with bivalent cations increase slightly the interactions of CO2 molecule with adsorbents and/or cationic site. Indeed, the desorption energies of physisorbed CO2 obtained on the reference zeolite NaX (13.5 kJ·mol-1) are lower than that of exchanged zeolites E-CaX and E-BaX (15.77 and 15.17 kJ·mol-1 respectively). In the chemisorbed CO2 region (573 - 873 K), the desorption energies related to desorbed species (bidentate carbonates: CO32-) on the exchanged zeolites E-CaX and E-BaX are about 81 kJ·mol-1, higher than the desorbed species (bicarbonates: HCO32-) on the reference R-NaX (62 kJ·mol-1). In addition, the exchanged E-BaX zeolite develops the secondary adsorption sites corresponding to bicarbonates species with desorption energies of 35 kJ·mol-1 lower to desorption energies of bicarbonates noted on the reference zeolite NaX.

Getters: From Classification to Materials Design

The demand for getters with high sorption efficiency has generated a need for resources to assist in qualification of getter materials for their practical use. This paper discusses innovative steps which should provide a dramatic improvement in the selection and application of getter technologies used in various processes. The first step was to build a natural classification of chemisorbents, from which we obtain a corresponding order of suitability related to known getter products. The classification system suggested by the authors is based on criteria which are directly connected with the sorption behavior of the material. This has lead to the challenge of developing of a computing algorithm for characterization of sorption properties of getter materials and for solving the inverse problem—the problem of designing a chemisorbent based on the requirements of a fully realized application. The employment of the new methodology is demonstrated in the example of the calculations supporting the selection of getter films for MEMS.

Surface microstructure-controlled ZrO_(2) for highly sensitive room-temperature NO2 sensors

The high sensitivity of room-temperature gas sensors is the key to innovation in the areas of environment,energy conservation and safety.However,metal-oxide-based sensors generally operate at high temperatures.Herein,we designed three ZrO_(2)-based sensors and explored their NO_(2)sensing properties at room temperature.ZrO_(2)with three different morphologies and microstructure were synthesized by simple hydrothermal methods.The microstructures of sensing materials are expected to significantly affect gas sensing properties.The rod-shaped ZrO_(2)(ZrO_(2)-R)displayed the advantages such as higher crystallinity,larger pore size,narrower band gap and more chemisorbed adsorbed oxygen,compared to hollow sphere-shaped ZrO_(2)(ZrO_(2)-HS),stellate-shaped ZrO_(2)(ZrO_(2)–S).The ZrO_(2)-R sensor showed the highest response towards 30 ppm NO_(2)(423.8%)at room temperature,and a quite high sensitivity of 198.0%for detecting 5 ppm NO_(2).Although ZrO_(2)-HS and ZrO_(2)–S sensors exhibited lower response towards 30 ppm NO_(2)(232.9%and 245.1%),the response time and recovery time of these two sensors are 5 s/19 s and 4 s/3 s,respectively.This work can provide a new strategy for the development of roomtemperature metal-oxide-based sensors.

Electronic Structures of O_2 Molecules Chemisorbed on a(8,0) SWNT with Different Oxygen Contents:A Density Functional Theory Study

We report a theoretical study on the electronic structures of O2 chemisorbed on a（8,0） SWNT with different oxygen contents of 6.25,12.5 and 25%,respectively.On the basis of DFT calculations,we find that eight O2 molecules chemisorbed on the（8,0） SWNT aligned in the middle row of the circumference of the tube in proportional spacing way,is seen to become metallic,and a significant increase in conductivity is expected.There are different electronic structures of the functionalized systems related to different oxygen contents or O2 molecules＇ chemisorbed positions.

Chemisorbed dimethylammonium chlorochromate as selective oxidants for primary and second aryAlcohols

Two new reagents. dimethylammonium chlorochromale adsrbed on alumina and silicagel are describe as convenient reagents for efficient oxidation of a variety of primary and secondaryalcohols. These two reagents are very stable and call be safely used for the oxidation of alcoholscontaining double bond.

EHMO Studies of Chemisorbed Dioxygen Species on Na＿2O and K＿2O and of Their Interaction with CH＿4 and CH＿3－Radical

ith an improved EHMO method, three modes (flat-lying, vertical , and in-clined insertion) for adsorption and activation of dioxygen on (100) , (110) and(111) surfaces of Na_2O and of K,O have been exaniinecl, and the interaction ofthese dioxygen adspecies with CH_4 and with CH_3 · (radical) from gas pliase liasbeen investigated. The results indicate that both oxides tend to forni less cliargedadspecies of dioxygen, with the flat-lying adsorption on (110) surface most favor-able energetically. All these cliemisorbed dioxygen species are capable of interactingeffectively with CH_4 and Abstract ing one hydrogen atom from the CH_4 molecule andtheir tendencies to reassociate with CH_3 · , which would easily lead to deep oxida-tion of the fragments of hydrocarbons, are enhanced with inereasing negativecliarges on them. In comparison with Na_2O, K_2O has a little stronger tendency tostabilize less charged dioxygen adspecies; this has a close relation with the knownexperimental fact that K￣+ showed better promoting effect than Na￣+ in improvingC_2-selectivity in methane oxidative coupling (MOC ).

Studies of Catalysis in Partial Oxidation of Methane to Syngas（Ⅱ）──Chemisorbed Species，Energetics and Mechanism

he characteristic study,by means of in-situ IR spectroscopy, of chemisorbed species on the Ni-catalysts for the partial oxidation of methane(POM)to syngas demonstrated the existence of CH_x(a)and H_xCO(a)adspecies on the functioning Ni-catalysts, Several designed experimental investigations on the reactivities of methane with CO_2 and with O_2,respectively,over the Ni-catalysts, and of CO_2 with the prereduced Ni-catalyst,ats well as of the deposited carbon with CO_2 and with O_2,respectlvely,liave been carried out and the reLqults were unfavorable to the two-step mechanistic interpretation proposed for the POM reaction. By means of tlie BOC-MP Approach,energetics of a set of elementary reactions,which may be involved in the POM process,on the clean(111)surface of Ni,Fe,Cu and Pd, re- spectively,has been studied.The result;of the experiments and the calculation of the present work favor the direct catalytic dissociation-plus-surface oxidation-plus-further debdrogenation mechanism as the dominant pathway making major contribution to the POM reaction.