TPD Spectra Research Articles

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.

Green synthesis of SrO bridged LaFeO3/g-C3N4 nanocomposites for CO2 conversion and bisphenol A degradation with new insights into mechanism

Very recently the green synthesis routes of nanomaterials have attracted massive attention as it overcome the sustainability concerns of conventional synthesis approaches. With this heed, in this novel research work we have synthesized the g-C3N4 nanosheets based nanocomposites by utilizing Eriobotrya japonica as mediator and stabilizer agent. Our designed bio-caped and green g-C3N4 nanosheets based nanocomposites have abundant organic functional groups, activated surface and strong adsorption capability which are very favorable for conversion CO2 into useful products and bisphenol A degradation. Beneficial to further upgrade the performances of g-C3N4 nanosheets, the resulting pristine g-C3N4 nanosheets are coupled with LaFeO3 nanosheets via SrO bridge. Based on our experimental results such as TEM, XRD, DRS, TPD, TGA, PL, PEC and FS spectra linked with OH amount it is confirmed that the biologically mediated green g-C3N4 nanosheets are eco-friendly, highly efficient and stable. Furthermore, the coupling of LaFeO3 nanosheets enlarged the surface area, enhanced the charge separation, while the insertion of SrO bridge worked as facilitator for electron transportation and photo-electron modulation. In contrast to pristine green g-C3N4 nanosheets (GCN), the activities of final resulting sample 6LFOS-(4SrO)-GCN are improved by 8.0 times for CO2 conversion (CH4 = 4.2, CO = 9.2 μmol g−1 h−1) and 2.5-fold for bisphenol A degradation (88%) respectively. More specifically, our current research work will open a new gateway to design cost effective, eco-friendly and biological inspired green nanomaterials for CO2 conversion and organic pollutants degradation which will further support the net zero carbon emission manifesto and the optimization of carbon neutrality level.

Synthesis of phosphate-bridged g-C3N4/LaFeO3 nanosheets Z-scheme nanocomposites as efficient visible photocatalysts for CO2 reduction and malachite green degradation

In this novel study, phosphate bridged p-type LaFeO3 nanosheets and n-type g-C3N4 nanosheets Z-scheme nanocomposites are successfully designed. Herein, our results confirmed that LaFeO3 nanosheets and g-C3N4 nanosheets have excellent performances as compared to nanosized LaFeO3 and g-C3N4 nanoparticles respectively. Based on TEM, HRTEM with elemental mapping, XRD, DRS, XPS, TR-PL, FTIR, TPD, PEC, BET and FS spectra related to •OH amount have confirmed that the fabrication of g-C3N4 nanosheets has successfully enhanced the charge separation and enlarged the surface area of LaFeO3 nanosheets. Correspondingly, the interfacing of phosphate bridge (P-O) with strong shuttling ability worked as linker and facilitator for photogenerated charge transfer and enhancement. In contrast to pristine LaFeO3 nanosheets (LFONS), the amount optimized resulting 15CNNS-3P-LFONS nanocomposites have 6-fold and 3.5-fold improvement in activities for CO2 reduction and malachite green degradation respectively. Based on scavenger experiments related to active species and photocatalytic pollutants degradation pathway mechanism, it is confirmed that h+ and •O2- is the vital species for malachite green degradation. Finally, we believe that our current novel research studies will open a new gateway for the synthesis of p-LaFeO3 and n-g-C3N4 type based Z-scheme and its utilization for energy production and environmental remediation.

Cross-metathesis of methyl oleate with ethylene over methyltrioxorhenium supported on ZnAl2O4 as a heterogeneous catalyst

A new heterogeneous catalyst system for the cross-metathesis of methyl oleate with ethylene was investigated based on methyltrioxorhenium (MTO) grafted on the spinel-type mesoporous ZnAl2O4 in the absence of chloride for the first time. NH3 TPD spectra revealed that the number of Lewis acid sites of ZnAl2O4 decreased significantly after MTO grafting, thereby demonstrating that the Lewis acid sites of the ZnAl2O4 support are involved in the binding to MTO. Notably, the MTO grafted on ZnAl2O4 catalyst exhibited a good catalytic activity, producing only the desired cross-metathesis products of 1-decene and methyl 9-decenoate.

Quantitative Relationship Between Activity and Acid Site Distribution in the Oligomerization of Ethylene Over MCM-41 Catalyst

Nickel ion exchanged MCM-41 samples with different Si/Al ratios and Ni-ZSM-5/MCM-41 were prepared and used to catalyze ethylene oligomerization which was performed in a fixed bed model (T = 523 K, P = 2 MPa). A temperature programmed desorption of ammonia (NH3-TPD) method was employed to quantitatively determine the acid strength distribution of Ni-MCM-41 samples with different Si/Al ratios and Ni-ZSM-5/MCM-41. The TPD spectrum was analyzed by an interrupted-TPD method with desorption-control (dc-method) to obtain the desorption activation energy of ammonia, which can be used as acid strength scale for the purpose of correlation with catalytic activity. A quantitative relationship between catalyst acidity and catalytic activity was established by a Bronsted type equation. The site with desorption activation energy of ammonia E = 124 kJ mol−1 was found as the most suitable site for ethylene oligomerization. An approximate linear relationship is obtained between the activity of the ethylene oligomerization reaction and the acid amount corresponding to the acid site with E = 124 kJ mol−1.

Temperature Programmed Oxygen Desorption and Sorption Processes on Pr2-XLaxNiO4+ δ Nickelates

The present work is devoted to the investigation of temperature programmed oxygen desorption - sorption (TPD) processes performed on SOFC innovative cathode materials with Pr2-xLaxNiO4+δ composition. The experiments were performed using the coulometric titration technique involving an OXYLYT™ device, over the temperature cycle 20 – 900 – 20 °C. The considered parameters were the time and temperature dependences of both the titration current and the oxygen over-stoichiometry. TPD spectra of Pr2-xLaxNiO4+δ (x ≠ 0) exhibited two sharp peaks (maxima) of titration current with excellent resolution at p(O2) = 50 Pa, induced by removal of oxygen from different sites of the crystal lattice. TPD spectrum of Pr2NiO4+δ recorded under the same conditions drastically differs from the spectra of Pr2-xLaxNiO4+δ as four sharp maxima of titration current are detected. The TPD spectra of Pr2-xLaxNiO4+δ then strongly depend on the nature of the rare-earth (La or Pr) in link with the oxygen over-stoichiometry amount.

Investigation of hydrogen isotope retention mechanisms in beryllium: High resolution TPD measurements

Abstract The retention of ion-implanted deuterium in beryllium poly- and single crystals at room temperature is studied using high precision temperature programmed desorption spectroscopy (TPD). Slow temperature ramps of 0.01 K/s in combination with well-defined experimental conditions are used to resolve the low temperature desorption regime for the first time revealing three sharp desorption peaks. The comparison to results of a coupled reaction diffusion system (CRDS) model shows, that the corresponding release mechanisms cannot be described by thermally activated rate processes. SEM images of a polycrystalline beryllium sample after implantation of deuterium with 2 keV per D atom show the formation of blisters of roughly 1 µm in diameter. Additionally, cracks on top of the blisters are found as well as spots, on which blisters are peeled off. Both processes are discussed to play a role in the low temperature release regime of the retained deuterium. Investigation of TPD spectra performed on single crystalline beryllium shows a jagged pattern in the low temperature release regime, which can be connected to blisters bursting up, releasing big amounts of deuterium in short time scales.

Effects of preparation conditions on the performance of simultaneous desulfurization and denitrification over SiO 2 -MnO x composites

Abstract SiO2-MnOx composites were prepared by sol-gel method and used to simultaneously desulfurization and denitrification. The effects of TEOS (tetraethoxysilane) concentration, H2O concentration and ammonia concentration on the performance of simultaneous desulfurization and denitrification over the SiO2-MnOx composites were investigated. The experiment results showed that all of the SiO2-MnOx composites with a desulfurization efficiency of up to 100% in the experiment, while the denitrification efficiency was decreased from nearly 100% with the increasing of time. The SiO2-MnOx composite which was synthesized with 0.054 mol TEOS, 1.111 mol H2O, and 0.208 mol ammonia (TEOS: ammonia: H2O = 1.0: 3.9: 20.6) exhibited the best adsorption capacities of SO2 and NO, and the adsorption capacities of SO2 and NO were 0.0680 mmol/g and 0.1010mmoxl/g, respectively. The structure of the SiO2-MnOx composites, SiO2 distributed uniformly on the surface of MnOx, could reduce the adsorption inhibition of SO2 on NO, which was due to most of the SO2 could be adsorbed by the outer material (SiO2), while most of the NO molecules and the remaining SO2 enter into the inner layer and be adsorbed by MnOx. The urea treatment can increase the pore structure of the material by decomposing to produce NH3 and CO2, which made it easier for the gas to enter the material inside and improved the adsorption capacity of SO2 and NO. Based on the analysis of the TPD and FTIR spectra, it was apparent that the product of chemisorption was manganese nitrate, sulfuric acid and manganese sulfate.

Acidity, oxophilicity and hydrogen sticking probability of supported metal catalysts for hydrodeoxygenation process

Hydrodeoxygenation is an oxygen removal process that occurs in the presence of hydrogen and catalysts. This study has shown the importance of acidity, oxophilicity and hydrogen sticking probability of supported metal catalysts in having high hydrodeoxygenation activity and selectivity. These properties are required to ensure the catalyst has high affinity for C-O or C=O bonds and the capability for the adsorption and activation of H2 and O-containing compounds. A theoretical framework of temperature programmed desorption technique was also discussed for the quantitative understanding of these properties. By using NH3-TPD, the nature and abundance of acid sites of catalyst can be determined. By using H2-TPD, the nature and abundance of metallic sites can also be determined. The desorption activation energy could also be determined based on the Redhead analysis of TPD spectra with different heating rates.

High-temperature and short-time hydrothermal fabrication of nanostructured ZSM-5 catalyst with suitable pore geometry and strong intrinsic acidity used in methanol to light olefins conversion

High temperature hydrothermal synthesis method was developed to preparation of nanostructured ZSM-5 molecular sieves at short crystallization time. A series of catalysts were synthesized at various temperatures and crystallization times for achievement of pure ZSM-5 phase with MFI structure. The synthesized catalysts were investigated with XRD, FESEM, EDX, BET-BJH, FTIR and TPD-NH3 techniques. The results revealed that hydrothermal synthesis conditions generally affected the nucleation rate, particle size, textural properties and acidic nature of ZSM-5 catalysts. It was found that pure ZSM-5 materials with high crystallinity could be obtained at specific crystallization conditions of about 300 °C for 1.5 h and also 350 °C for 0.5 h. Increasing the hydrothermal temperature to 350 °C and decreasing the crystallization time to 0.5 h led to the formation of small particles with high specific surface area of 392 m2/g. Furthermore, ammonia TPD spectra showed that ZSM-5(300-1.5) catalyst contained higher amount of acid sites and less acid strength compared to ZSM-5(350-0.5) catalyst. The catalytic performance of samples was studied for conversion of methanol to light olefins under different reaction conditions. Interestingly, the proper pore geometry along with the strong intrinsic acidity resulted in a tendency for excessive production of light olefins for ZSM-5(350-0.5) catalyst. The selectivity of light olefins over this catalyst was increased about 94% in the long time on stream (2100 min). Also, the possible reaction pathway for ZSM-5 synthesis at high temperatures was discussed in details.

CO adsorption on W(100) during temperature-programmed desorption: A combined density functional theory and kinetic Monte Carlo study

Using a combined density functional theory (DFT) and kinetic Monte Carlo (KMC) simulations, we study the adsorption at 800K and subsequent desorption of CO on W(100) at higher temperatures. The resulting TPD profiles are known experimentally to exhibit three desorption peaks β1, β2, and β3 at 930K, 1070K, and 1375K, respectively. Unlike more recent theoretical studies that propose that all three aforementioned peaks are molecularly rather than associatively desorbed, our KMC analyses are in support of the latter, since at 800K dissociation is facile and that CO exists as dissociation fragments C and O. We show that these peaks arise from desorption from the same adsorption site but whose binding energy varies depending on local environment, that is, the presence of CO as well as dissociation fragments C and O nearby. Furthermore we show that several key parameters, such as desorption, dissociation and recombination barriers all play a key role in the TPD spectra—these parameter effectively controls not only the location of the TPD peaks but the shape and width of the desorption peaks as well. Moreover, our KMC simulations reveal that varying the heating rate shifts the peaks but leaves their shape intact.

Experimental Research on the Adsorption Behavior of NH<sub>3</sub> at the Surface of CaO

Temperature programed desorption experiments were carried out for analyzing the TPD spectra of NH3 desorbed by CaO at different temperature ramp, pressure, and different ratio of CaO to CaSO4. Moreover, factors affecting on the adsorption process were analyzed. Based on the activation energy of He, NH3 desorbed at the CaO surface was estimated by experimental spectra and the TPD model.

Mo+TiO2(110) Mixed Oxide Layer: Structure and Reactivity

We present a STM/XPS/TPD/LEED study of the structural and electronic properties of Mo+Ti mixed oxide layers on TiO2(110), and of their interaction with water, methanol and ethanol. Several different preparation procedures were tested and layers with different degrees of Mo/Ti mixing were prepared. Ordered mixed oxide surface phases with distinct LEED patterns could not be found; for all investigated Mo concentrations a TiO2(110) like pattern was observed. Mo tends to agglomerate on the surface where it is found predominantly as Mo6+ at low coverages and as Mo4+ at high coverages. Mo4+ was also identified in the bulk of the mixed oxide layer. The Mo3d binding energies categorize the Mo4+ species as being dimeric. A third Mo3d doublet is attributed to a Mo species (Mon+) with an oxidation state between those reported for Mo in MoO2 and metallic Mo. Two types of Mo-induced features could be identified in the STM images for low Mo concentrations (in the range of 1 %). At higher Mo concentrations (~50 %) the surface is characterized by stripes with limited lengths in [001] direction. The concentration of bridging oxygen vacancies, which are common defects on TiO2(110), is reduced significantly even at low Mo concentrations. Methanol and ethanol TPD spectra reflect this effect by a decrease of the intensity of the features related to these surface defects. At elevated MoOx coverages, the yield of reaction products in methanol and ethanol TPD spectra are somewhat smaller than those found for clean TiO2(110) and the reactions occur at lower temperature.

Surface reactivity of oxide phases generated on Pd(111) during the growth vs. reduction of PdO(101) films

We used temperature programmed reaction spectroscopy (TPRS) to investigate the adsorption and complete oxidation of propane on various surface oxygen phases which evolve during the growth and reduction of PdO(101) films on Pd(111). Desorption spectra reveal clear differences in the binding of molecular propane on the different oxygen phases investigated, including the p(2×2)-O chemisorbed phase on Pd(111), two-dimensional (2D) oxide(s) and multilayer PdO(101) thin films. We find that propane reacts to an immeasurable extent on the p(2×2)-O and 2D oxide phases during TPRS, while reaction is facile on the PdO(101) surface. For the partially oxidized and reduced surfaces, we find that the CO2 product yield obtained from propane-saturated surfaces increases continuously with increasing oxygen coverage above about 1 ML (monolayer), and observe a hysteresis in the surface reactivity such that more CO2 is produced when a given oxygen coverage is generated during the growth vs. reduction of a thin PdO(101) film. We show that the fractional areas of coexisting oxygen phases can be estimated by fitting propane TPD spectra obtained from partially oxidized surfaces with propane TPD spectra obtained from well-defined reference surfaces. Based on the estimated surface area fractions, we find that the CO2 product yields scale linearly with the amount of PdO(101) at the surface, irrespective of the types and amounts of coexisting phases, and show that the observed hysteresis arises from differences in the PdO(101) surface fractions obtained at a given coverage during growth and reduction of PdO(101) films. The estimated surface fractions also reveal that 2D oxide domains develop during the first stage of PdO(101) reduction, while metallic surface domains become prevalent only during the latter half of the oxide reduction process. A key finding is that the activation of propane on partially oxidized Pd(111) is relatively insensitive to the complexity of the surface phase distribution, and depends almost exclusively on the amount of PdO(101) domains that are present.

Porous MgH2/C composite with fast hydrogen storage kinetics

A porous MgH2/C composite can be synthesized through decomposition of an organo-magnesium precursor under hydrogen pressure. XRD patterns of the porous MgH2/C composite exhibit a pure MgH2 phase with a tetragonal structure. The morphology of the resulted samples is significantly dependent on the synthesis temperature and hydrogen pressure. The samples exhibit a rod-like structure and composed of nano-crystallites of MgH2 with a size of less than 5 nm. TPD spectra of a sample synthesized at 220 °C for 4 h show a remarkable decrease of the onset hydrogen release temperature. Further, this sample also exhibits fast hydrogen adsorption kinetics adsorbing 6 wt % of hydrogen in 3 min at 250 °C. The same amount of hydrogen is adsorbed in 11 min at 200 °C and 40 min at 150 °C, respectively. N2 physisorption measurements of this sample indicate meso-porosity with a BET surface area of 40.9 m2 g−1 and an average pore diameter of 20 nm.

Liquid phase oxidation kinetics of an ex-cellulose activated carbon cloth by NaOCl

The oxidation kinetics at ambient temperature of an ex-cellulose activated carbon cloth has been investigated using an aqueous solution of NaOCl. Oxidized samples were weighed and characterized by TG–TPD–MS and XPS. Weight analysis revealed three stages during the course of oxidation. The first is dominated by the creation of oxygen groups at the carbon surface with an initial oxygen uptake rate assessed at 20mgg−1min−1. The second involves a transfer of oxygenated carbonaceous matter to the liquid phase. The third corresponds to the degradation of the carbon fabric. The diameter of the fibers does not change during the first stage and decreases during the last two stages. The amount of oxygen groups fixed per gram of sample increases with oxidation time during the first two stages, and decreases during the third stage. The creation of oxygen groups progresses from the surface to the bulk. The oxidation degree of carbon atoms (CI–CIII) increases during oxidation. TPD spectra, including for water, have been examined in light of the recent literature and of the temperature-programmed surface reaction theory. The degradation of fibers is interpreted by the aromatic ring cleavage accompanying the creation of carboxylic groups.

Enantiospecific Adsorption of (R)-3-Methylcyclohexanone on Naturally Chiral Surfaces Vicinal to Cu(110)

(R)-3-methylcyclohexanone (R-3MCHO) has been shown to adsorb enantiospecifically on naturally chiral Cu surfaces vicinal to the Cu(110) plane. Adsorption of R-3MCHO on seven Cu single crystal surfaces vicinal to (110) was studied using temperature programmed desorption. These surfaces include Cu(110), Cu(771), Cu(430), Cu(13,9,1)R&S and Cu(651)R&S. The Cu(13,9,1)R&S and Cu(651)R&S surfaces are naturally chiral surfaces with terrace-step-kink structures. Enantioselective adsorption of R-3MCHO takes place on the chiral kink sites of these surfaces. Three R-3MCHO desorption features were resolved in the TPD spectra on Cu(13,9,1)R&S and Cu(651)R&S surfaces. Based upon comparisons between these and other Cu single crystal surfaces, they were assigned to desorption of R-3MCHO from flat terrace, close-packed step and kink sites. The desorption of R-3MCHO from the row and trough structure of the Cu(110) surface resembled desorption from a step structure rather than from a flat Cu(111) terrace. R-3MCHO desorbs enantiospecifically from the Cu(13,9,1)R&S and Cu(651)R&S surfaces. The peaks associated with R-3MCHO desorbing from the R- and S-chiral kink sites on Cu(13,9,1)R&S differed in temperature by 2.4 ± 0.8 K. This corresponds to an enantiospecific difference in the desorption energies of 0.7 ± 0.2 kJ/mol, with a preference for R-3MCHO adsorption at the R-kinks. In contrast, R-3MCHO has a desorption energy from the S-kinks on the Cu(651)S surface that is 0.7 ± 0.2 kJ/mol higher than from the R-kinks on the Cu(651)R surface.

FT-IR study of the surface redox states on platinum-potassium-alumina catalysts

Pt-K/Al2O3 (Pt 1%; K 5.4% wt/wt) catalyst active for the simultaneous Diesel particulate oxidation and NOx reduction have been characterized in comparison with 1% Pt/Al2O3 catalyst. IR spectra of adsorbed CO at −140°C and at room temperature allowed the detection of oxidized Pt centers and of their very strong oxidizing ability. TPD and IR spectra of adsorbed CO2 allowed to characterize the basicity of the samples. The data indicate that Pt centers lie in close proximity of potassium oxide species generating basicity.

Activation of Amberlyst-70 for Alkene Oligomerization in Hydrophobic Media

We have observed that pretreating Amberlyst-70 with a C9 ketone improves, up to five times, the rate of alkene oligomerization. Physical characterization of Amberlyst-70 reveals minimal changes to the particle dimensions upon exposure to 5-nonanone. Diffuse reflectance infrared spectroscopy indicates an interaction between the ketone and the acid sites within the catalyst. While the total number of acid sites is similar before and after treatment with nonanone, microcalorimetric studies of butene adsorption and temperature programmed desorption studies of butene desorption reveal that both adsorption and desorption of butene occur more rapidly in the catalyst treated with 5-nonanone, indicating that pretreatment of the catalyst with the ketone decreases the barrier for butene transport by 5–6 kJ/mol. The peak temperature for TPD spectra of butene desorption are observed to shift from 360 K for nonanone-treated Amberlyst-70 to 376 K in the case of untreated sample. The catalytic effect of the treatment with nonanone decreases slowly with time-on-stream, but remains after 200 h on stream (with the rate still being a factor of 2 higher than for the untreated sample); however, catalytic activity can be recovered upon additional treatment with ketone.

Adsorption of oxygen-containing aromatics used in petrochemical, pharmaceutical and food industries by means of lignin based active carbons

The adsorption processes of three aromatic chemicals onto activated carbons (ACs) from aqueous solutions have been studied. Eucalyptus kraft lignin obtained from cellulose industry as a residual biomass has been used to prepare activated carbons by physical activation with CO2. The influences of the activation time on the surface areas and pore volumes of the ACs were analyzed. The physicochemical properties and the surface chemical structure of the adsorbents have been studied by means of N2 and CO2 adsorption, ultimate analysis, XPS, TPD and SEM. XPS and TPD spectra of the ACs have suggested the presence of aromatic rings and carbon-oxygen functional groups in the solid surfaces. The potential use of the ACs for the removal of acetaminophen (paracetamol), salicylic acid and benzoic acid has been investigated at different pH, temperature and contact time. The adsorption equilibrium data have been correlated to Langmuir isotherm model. The thermodynamic study has been developed, the values of ΔH, ΔG, and ΔS have been calculated and they indicated that the processes are endothermic for acetaminophen and exothermic for salicylic and benzoic acids. The analysis of the kinetic experiments showed that the effective diffusivities are low; 10−12 to 10−11 cm2/s, and they are the corresponding to intraparticle mass transfer, which appears as the controlling step for the net adsorption processes.