Temperature-programmed Desorption Studies Research Articles

The influence of the potassium promoter on the kinetics and thermodynamics of CO adsorption on a bulk iron catalyst applied in Fischer–Tropsch synthesis: a quantitative adsorption calorimetry, temperature-programmed desorption, and surface hydrogenation study

The adsorption of carbon monoxide on an either unpromoted or potassium-promoted bulk iron catalyst was investigated at 303 K and 613 K by means of pulse chemisorption, adsorption calorimetry, temperature-programmed desorption and temperature-programmed surface reaction in hydrogen. CO was found to adsorb mainly molecularly in the absence of H(2) at 303 K, whereas the presence of H(2) induced CO dissociation at higher temperatures leading to the formation of CH(4) and H(2)O. The hydrogenation of atomic oxygen chemisorbed on metallic iron was found to occur faster than the hydrogenation of atomically adsorbed carbon. At 613 K CO adsorption occurred only dissociatively followed by recombinative CO(2) formation according to C(ads) + 2O(ads)→ CO(2(g)). The presence of the potassium promoter on the catalyst surface led to an increasing strength of the Fe-C bond both at 303 K and 613 K: the initial differential heat of molecular CO adsorption on the pure iron catalyst at 303 K amounted to 102 kJ mol(-1), whereas it increased to 110 kJ mol(-1) on the potassium-promoted sample, and the initial differential heat of dissociative CO adsorption on the unpromoted iron catalyst at 613 K amounted to 165 kJ mol(-1), which increased to 225 kJ mol(-1) in the presence of potassium. The calorimetric CO adsorption experiments also reveal a change of the energetic distribution of the CO adsorption sites present on the catalyst surface induced by the potassium promoter, which was found to block a fraction of the CO adsorption sites.

TPD and TPSR studies of formaldehyde adsorption and surface reaction activity over Ag/MCM-41 catalysts

The adsorption and surface reaction activity of formaldehyde were studied on the Ag/MCM-41 catalysts with different silver loadings by temperature-programmed desorption (TPD) and temperature-programmed surface reaction (TPSR) methods. It appeared that the silver loading had strong influence on the adsorption and surface reaction activity of HCHO. The addition of silver active species provided new adsorption site for the HCHO at low temperature, and its desorption temperature moved to lower temperature with the increase of silver loading to 8 wt%. With the further increase of silver loading, the desorption temperature of HCHO shifted to higher temperatures, which could be due to the aggregation of silver particles on the surface of the support. Moreover the quantity of adsorbed HCHO at higher silver loading (>8 wt%) changed inversely with the increase of silver content. TPSR experiments indicated that the surface reaction activity for HCHO oxidation was proportional with the adsorption performance of HCHO over Ag/MCM-41 catalysts with different silver loadings, and 8Ag/MCM-41 catalyst showed highest surface reaction activity for HCHO oxidation. Thus it is reasonable to suggest that an appropriate silver loading and particle dispersion would be essential to obtain high catalytic activity for HCHO oxidation at low temperatures.

Reaction of Formic Acid over Amorphous Manganese Oxide Catalytic Systems: An In Situ Study

The interaction of formic acid with amorphous manganese oxide (AMO) is investigated using in situ photoelectron and infrared spectroscopy techniques. Soft X-ray photoelectron spectroscopy (sXPS) and in situ FTIR illustrate two possible modes of formate bound species at the AMO surface. Two peaks in the IR region from 1340−1390 cm−1 are indicative of formate species bound to the surface in a bidentate configuration. However, a 224 cm−1 band gap between νsOCO and νasOCO suggests formate is bound in a bridging configuration. Temperature-programmed desorption studies confirm the formate bound species desorbs as carbon dioxide from the surface at multiple binding sites. At temperatures above 700 K, the presence of K+···OC complex suggests the bound species interacts at vacant sites related to framework oxygen and cation mobility.

Adsorption Site Distributions on Cu(111), Cu(221), and Cu(643) as Determined by Xe Adsorption

Xe has been used to probe the distributions of adsorption sites across three different Cu single-crystal surfaces: Cu(111), Cu(221), and Cu(643). These expose terrace, step, and kink sites, respectively. The study couples the use of scanning tunneling microscopy (STM), temperature-programmed desorption (TPD), and photoemission of adsorbed Xe (PAX) to assess their use as methods for determining adsorption site distributions on Cu surfaces. STM shows that the Xe adsorption sites in order of energetic preference are kink, step edge, and terrace, but indicates that the binding energy differences between the three are likely very small. This is borne out by Xe TPD studies that show distinct differences in the desorption kinetics on the three surfaces but unresolvable differences in the desorption temperatures and binding energies at the terrace, step, and kink sites. PAX spectra reveal observable features that can be associated with Xe adsorption at terrace, step, and kink sites. These features can be analyzed...

Effect of water on formic acid photocatalytic decomposition on TiO 2 and Pt/TiO 2

The effect of water on the adsorption and photocatalytic decomposition (PCD) of formic acid on TiO 2 and Pt/TiO 2 was investigated using transient reaction studies, temperature-programmed desorption (TPD), and Fourier transform infrared (FTIR) spectroscopy. Reaction studies indicated that physisorbed water increased the PCD rate of formic acid to a small extent on TiO 2 and to a major extent on Pt/TiO 2, but the presence of only chemisorbed water did not. FTIR spectroscopy and TPD studies indicate that the main effect of the addition of water to TiO 2 that had adsorbed formic acid was the displacement of formic acid. However, FTIR spectroscopy indicated that the addition of water caused a change in the adsorbed structure of formate that may be associated with the higher reactivity. These transformations can have an important influence on elementary steps in the photocatalytic decomposition of formic acid on TiO 2 and Pt/TiO 2.

ChemInform Abstract: Oxidation of NH3 Over YBa2Cu3O7(123) Oxide Systems.

Abstract A temperature-programmed desorption study showed that the activation energy of oxygen desorption from YBa 2 Cu 3 O 7− x ( x = 0.05), PrBa 2 Cu 3 O 7− x ( x =0.02), and YBa 2 Cu 2 CoO 7− x ( x = 0.26) were 28.2, 26.4, and 22.3 kcal/mole, respectively. Anaerobic oxidation of NH 3 over these oxide systems shows the formation of H20, N 2 and NO transforming the oxides to tetragonal phases. Aerobic oxidation of NH 3 is NO specific over all the three oxide catalysts. The Co-substituted YBa 2 Cu 2 CoO 7+ x was the most reactive and stable oxide in this family; the lower oxygen desorption energy and higher reactivity are suggested to be due to the presence of holes in the form Co 4+ O 2− ⤤ Co 3+ O − . The conversion of NH 3 to NO was nearly 100% above 400°C when the ammonia flow rates were 10 μmole/cm 2 /s over 0.3 g of the YBa 2 Cu 2 CoO 7+ x catalyst. Structural Chemistry Unit.

SERS, SEIRA, TPD, and DFT Study of Cyanobenzoic Acid Isomer Film Growth on Silver Nanostructured Films and Powder

A combination of surface-enhanced infrared absorption (SEIRA), surface-enhanced Raman spectroscopy (SERS), temperature programmed desorption (TPD), and density functional theory (DFT) calculations ...

Dissociative and molecular oxygen chemisorption channels on reduced rutile TiO 2(110): An STM and TPD study

High-resolution scanning tunneling microscopy (STM) and temperature-programmed desorption (TPD) were used to study the interaction of O 2 with reduced TiO 2(110)–(1 × 1) crystals. STM is the technique of choice to unravel the relation between vacancy and non-vacancy assisted O 2 dissociation channels as a function of temperature. It is revealed that the vacancy-assisted, first O 2 dissociation channel is preferred at low temperature (~ 120 K), whereas the non-vacancy assisted, second O 2 dissociation channel operates at temperatures higher than 150 K–180 K. Based on the STM results on the two dissociative O 2 interaction channels and the TPD data, a new comprehensive model of the O 2 chemisorption on reduced TiO 2(110) is proposed. The model explains the relations between the two dissociative and the molecular O 2 interaction channels. The experimental data are interpreted by considering the available charge in the near-surface region of reduced TiO 2(110) crystals, the kinetics of the two O 2 dissociation channels as well as the kinetics of the diffusion and reaction of Ti interstitials.

Hydrogenation of Carbon Dioxide by Water: Alkali-Promoted Synthesis of Formate

Conversion of carbon dioxide utilizing protons from water decomposition is likely to provide a sustainable source of fuels and chemicals in the future. We present here a time-evolved infrared reflection absorption spectroscopy (IRAS) and temperature-programmed desorption (TPD) study of the reaction of CO2 + H2O in thin potassium layers. Reaction at temperatures below 200 K results in the hydrogenation of carbon dioxide to potassium formate. Thermal stability of the formate, together with its sequential transformation to oxalate and to carbonate, is monitored and discussed. The data of this model study suggest a dual promoter mechanism of the potassium: the activation of CO2 and the dissociation of water. Reaction at temperatures above 200 K, in contrast, is characterized by the absence of formate and the direct reaction of CO2 to oxalate, due to a drastic reduction of the sticking coefficient of water at higher temperatures.

Sulfonic acid functionalized mesoporous SBA-15 for one-pot synthesis of substituted aryl-14H-dibenzo xanthenes and bis(indolyl) methanes

The comparative catalytic activity studies of biologically and industrially important compounds such as Xanthenes and bis (indolyl) methanes were evaluated over propylsulfonic acid functionalized SBA-15/SO3H. The material was characterized via standard characterization techniques such as Powder X-ray diffraction, FTIR, Temperature programmed desorption studies of NH3. The catalytic performance of SBA/SO3H under environmentally benign conditions results in high yield of xanthenes compared to bis (indolyl) methanes and finally the mechanism for both the reactions were proposed.

A comparative study of Ba0.5Sr0.5Co0.8Fe0.2Ox (BSCF) and SrFeCo0.5Ox (SFC) ceramic membranes used for syngas production

Dense oxygen permeable ceramic membranes are promising materials for separating oxygen from air and for syngas production. In this work, the role of two different membrane materials, Ba0.5Sr0.5Co0.8Fe0.2Ox (BSCF) and SrFeCo0.5Ox (SFC), in the conversion of methane, has been studied. Pulse and temperature programmed desorption studies of CO and CO2 showed a higher CO and CO2 adsorption on BSCF compared to the SFC membrane. More CO adsorption resulted in more CO2 production. Raman spectroscopy of BSCF and SFC ceramic materials after CO and CO2 exposure showed carbonate species on these samples. Both H2 and O2 adsorption were significantly higher on BSCF, with significant water formation in the presence of hydrogen. Reaction investigations over Pt-based catalysts demonstrated higher methane conversion and a higher H2:CO ratio on the BSCF membrane than on the lower flux SFC membrane because of more interaction of the products with BSCF. Under reaction conditions, the simultaneous occurrence of steam and CO2 reforming of methane would lead to a higher methane conversion and a higher H2:CO ratio on BSCF. The onset temperature of oxygen release for BSCF was observed to be lower than that for SFC while the amount of oxygen release was significantly greater. These studies suggest that BSCF might be suitable for hydrocarbon conversion reactions at much lower temperatures than conventional dense ceramic membranes.

X-ray induced irradiation effects in glycine thin films: A time-dependent XPS and TPD study

The radiation-induced chemistry in ultrahigh vacuum (UHV)-sublimated thin glycine films during continuous soft X-ray irradiation was investigated by X-ray photoelectron spectroscopy (XPS) and temperature-programmed desorption (TPD). The glycine films were irradiated with an Al Kα X-ray source (1486.6 eV) for over 360 min and XPS spectra were taken repeatedly every 60 min. TPD measurements of pristine and X-ray exposed glycine layers were also conducted. The results show that the glycine films are very sensitive to damage by X-ray illumination. The analysis of C 1s, N 1s and O 1s spectral regions together with TPD changes indicate that amino acid degradation occurs mainly via dehydrogenation, decarboxylation, dehydration and deamination of pristine molecules. Among the decomposition products, H 2, CO 2, H 2O and NH 2 are identified. Enrichment of the X-ray exposed surface with hydrocarbon fragments is detected as well. The observed effects must be taken into account in studies of amino acids and peptides utilizing X-rays.

The adsorption and reaction of ethylene glycol and 1,2-propanediol on Pd(111): A TPD and HREELS study

The reactions of ethylene glycol and 1,2-propanediol have been studied on Pd(111) using temperature programmed desorption (TPD) and high resolution electron energy loss spectroscopy (HREELS). Both molecules initially decompose through O–H activation, forming ethylenedioxy (–OCH 2CH 2O–) and 1,2-propanedioxy (–OCH 2CH(CH 3)O–) surface intermediates. For ethylene glycol, increases in thermal energy lead to dehydrogenation and formation of carbonyl species at both oxygen atoms. The resulting glyoxal (O═CHCH═O) either desorbs molecularly or reacts through one of two competing pathways. The favored pathway proceeds via C–C bond scission, dehydrogenation, and decarbonylation to form carbon monoxide and hydrogen. In a minor pathway, small amounts of glyoxal undergo C–O bond scission and recombination with surface hydrogen to form ethylene and water. The same reaction mechanism occurs for 1,2-propanediol after methyl elimination and formation of glyoxal. However, this is accompanied by a minor pathway involving a methylglyoxal (O=CHC(CH 3)=O) intermediate. The prevalence of the dehydrogenation/decarbonylation pathway in the current work is consistent with the high selectivity for C–C scission in the aqueous phase reforming of polyols on supported Pd catalysts.

Production of hydrogen from dimethyl ether on supported Au catalysts

The adsorption and reactions of dimethyl ether (DME) were investigated on Au nanoparticles supported by various oxides and carbon Norit. Infrared spectroscopic and temperature programmed desorption studies revealed that DME adsorbs readily on most oxidic supports. A limited dissociation of DME to methoxy species was established on Au particles by IR spectroscopy. As regards the formation of hydrogen, Au/CeO 2 is the most effective catalyst. On Au/Al 2O 3 catalyst the main process was the formation of methanol with a very small amount of hydrogen. Deposition of Au on CeO 2–Al 2O 3 mixed oxide resulted in a very active catalyst for H 2 production. The yield for H 2 in the reforming of DME approached the value of 73% at 723–773 K. This feature was explained by the hydrolysis of DME to methanol on alumina, and the fast decomposition of methanol at the Au/CeO 2 interface. Adding potassium promoter to Au/CeO 2–Al 2O 3 catalyst further enhanced the production of hydrogen as indicated by the increase of the yield to ∼87%. No deactivation of the catalyst was experienced at 773 K for the measured time, ∼10 h.

Reversibility and Improved Hydrogen Release of Magnesium Borohydride

Desorption and subsequent rehydrogenation of Mg(BH4)2 with and without 5 mol % TiF3 and ScCl3 have been investigated. Temperature programmed desorption (TPD) experiments revealed a significant increase in the rate of desorption as well as the weight percentage of hydrogen released with additives upon heating to 300 °C. Stable Mg(BxHy)n intermediates were formed at 300 °C, whereas MgB2 was the major product when heated to 600 °C. These samples were then rehydrogenated and subsequently characterized with powder X-ray diffraction (pXRD), Raman, and NMR spectroscopy. We confirmed significant conversion of MgB2 to fully hydrogenated Mg(BH4)2 for the sample with and without additives. TPD and NMR studies revealed that the additives have a significant effect on the reaction pathway during both dehydrogenation and rehydrogenation reactions. This work suggests that the use of additives may provide a valid pathway for improving intrinsic hydrogen storage properties of magnesium borohydride.

Selective Adsorption and Thermal Evolution of Bifunctional Carboxylic Acids: Competition of O—H Dissociation and Other Reaction Products in Acrylic Acid and Propanoic Acid on Si(100)2×1

The dissociative adsorption of acrylic acid on Si(100)2×1 at room temperature has been investigated by X-ray photoelectron spectroscopy (XPS) and temperature programmed desorption (TPD), as well as density-functional theory (DFT) calculations. Three C 1s features can be attributed to the carboxyl C of bidentate acrylate (at 286.8 eV) and unidentate acrylate (at 289.3 eV), both resulting from O—H dissociation upon adsorption, and to their corresponding ethenyl C atoms (at 285.0 eV). The formation of bidentate acrylate at a low exposure is followed by that of unidentate acrylate at a higher exposure, with approximately equal populations for both adstructures at the saturation exposure. DFT calculations confirm that the bidentate acrylate adstructure gives the most stable adsorption structure configuration. The combined temperature-dependent XPS and TPD studies provide strong evidence for the formation of CO, ethylene, acetylene, and propene, with 60% of the C moiety from the adsorption configurations conver...

Combined XPS and TPD study of oxygen-functionalized carbon nanofibers grown on sintered metal fibers

A composite material consisting of carbon nanofibers (CNFs) grown on sintered metal fiber filters was modified by H 2O 2 or plasma-generated O 3. Coupling temperature programmed desorption (TPD) and X-ray photoelectron spectroscopy (XPS) techniques in the same UHV apparatus allowed the direct correlation of the nature of the created O-functional groups and their evolution as CO and CO 2 upon heating. The two oxidative treatments yielded different distributions of O-containing groups. The relative contribution of oxidized carbon was very low in the C1s region, hence the functional groups were more robustly analyzed through the O1s region. The comparison of the released oxygen by integration of the TPD CO, CO 2 and H 2O spectra with the intensity loss of the XPS O1s spectra showed good agreement. In order to fit the data adequately, the set of O1s spectra was deconvoluted in at least four peaks for the differently activated samples. Finally, it was shown that functional groups formed by H 2O 2-treatment (mostly non-phenolic OH groups) are more thermally stable than those formed by O 3-treatment. The latter treatment increases the concentration of carboxylic functionalities, which decompose at temperatures < 800 K; O 3-activated CNFs should therefore show a more pronounced acidic behavior.

The formation of nitrogen-containing functional groups on carbon nanotube surfaces: a quantitative XPS and TPD study

Nitrogen-containing functional groups were generated on the surface of partially oxidized multi-walled carbon nanotubes (CNTs) via post-treatment in ammonia. The treatment temperature was varied in order to tune the amount and type of nitrogen- and oxygen-containing functional groups, which were studied using high-resolution X-ray photoelectron spectroscopy (XPS) and temperature-programmed desorption (TPD). The surface defects on CNTs due to the incorporation of nitrogen were investigated by Raman spectroscopy. Deconvoluted XP N1s spectra were used for the quantification of different nitrogen-containing functional groups, and TPD studies were performed in inert and ammonia atmosphere to investigate the surface reactions occurring on the oxidized CNT surfaces quantitatively. Nitrile, lactam, imide and amine-type functional groups were formed in the presence of ammonia below 300 degrees C. When the OCNTs were treated in the medium temperature range between 300 degrees C to 500 degrees C, mainly pyridine-type nitrogen groups were generated, whereas pyridinic, pyrrolic and quaternary-type nitrogen groups were the dominating species present on the CNT surface when treated above 500 degrees C. It was found that about 38% of the oxygen functional groups react with ammonia below 500 degrees C.

Low-temperature selective catalytic reduction of NO with NH 3 over Mn [sbnd]Ce oxides supported on TiO 2 and Al 2O 3: A comparative study

Mn Ce oxides were supported on TiO 2 and Al 2O 3 by an ultrasonic impregnation method and used for selective catalytic reduction (SCR) of NO with NH 3 at low-temperature (80–220 °C). Mn Ce/TiO 2 showed a relatively higher SCR activity than Mn Ce/Al 2O 3 at the temperature range of 80–150 °C. When the reaction temperature was higher than 150 °C, Mn Ce/Al 2O 3 exhibited superior SCR activity to Mn Ce/TiO 2. NH 3 temperature programmed desorption study proved that Mn Ce/TiO 2 was mainly Lewis acidic, while Mn Ce/Al 2O 3 could provide more Brönsted acid sites. These acid sites play an important role in SCR according to in situ diffuse reflectance infrared transform spectroscopy (DRIFT) analysis. The main SCR reaction was a typical Eley–Rideal mechanism on Mn Ce/TiO 2, which took place between coordinated NH 3 / NH 4 + and gas-phase NO. For Mn Ce/Al 2O 3, the reaction mainly occurred via another pathway when the temperature exceeded 150 °C, which commenced with the adsorption and oxidation of NO and was followed by reaction between NO 2 or NO 2-containing compounds and NH 3 adspecies. This reaction pathway makes a significant contribution to the improved NO conversion for Mn Ce/Al 2O 3 at higher temperature.

Adsorption and Vibrations of α,β-Unsaturated Aldehydes on Pt(111) and Pt−Sn Alloy (111) Surfaces. 3. Adsorption Energy vs Adsorption Strength

Recently we presented high-resolution electron energy loss spectroscopy (HREELS) and temperature-programmed desorption (TPD) studies on the adsorption of prenal (3-methyl-2-butenal) and crotonaldeh...