Temperature-programmed Desorption Spectra Research Articles

Temperature-Programmed Desorption of Single Zeolite Nanoparticles.

Zeolites are essential solid acid catalysts in various chemical processes. Temperature-programmed desorption (TPD) is one of the most established techniques used to characterize the acidity of zeolites by measuring the desorption kinetics of probes from bulk samples. However, conventional TPD can hardly deliver the intrinsic acid properties of zeolites because the apparent desorption kinetics are inevitably mixed with mass transfer and thermal conduction due to the large sample amount (∼0.1 g). Herein, we developed an optical microscopy approach to measure the TPD spectra of single zeolite nanoparticles, termed oTPD, by in situ monitoring of the reduced scattering intensity of individuals as a result of the desorption of probe molecules during heating. A significantly reduced sample amount contributed to the oTPD spectrum, revealing an intrinsic desorption temperature of ∼300 °C lower than the apparent value and also a greatly narrowed peak width from ∼150 to ∼15 °C. Correlating oTPD and micro-Raman spectra of the very same individuals further uncovered a linear dependence between the acidity and the content of silicon islands. This study provided unprecedented capabilities for measuring the intrinsic acid properties and the desorption kinetics of single zeolite nanoparticles, with implications for better understanding the structure-acidity relationship and for designing better zeolite catalysts.

Effect of Bystander Hydrogen Atoms on Hydrogen Desorption on Single-Atom Alloy Surfaces: Insights from Simulated Temperature-Programmed Desorption Spectra.

Single-atom alloy (SAA) catalysts exhibit unique and excellent catalytic properties in heterogeneous hydrogenation/dehydrogenation reactions. A thorough understanding of the microscopic surface processes is essential to improve the catalytic performance. Here, from a new perspective of the temperature-programmed desorption (TPD) spectra of hydrogen (H) on two common SAA surfaces, Pt@Cu(111) and Pd@Cu(111), we reveal and confirm the key influence of H atoms attached to Pt/Pd dopants, i.e., the H atom bystander, on the desorption process of surface H atoms. It is found that only after considering the effect of the H atom bystander can the simulated TPD spectra well reproduce the experimentally observed higher desorption temperature on Pt@Cu(111) than on Pd@Cu(111) and the leftward shift of the TPD peak with increasing H atom coverage; otherwise, the features are inconsistent with experiments. Our work provides direct evidence for the effect of bystander H atoms from a simulation perspective.

Theoretical study of hydrogen desorption on the Ni(100) surface through simulated temperature programmed desorption spectra

Nickel has been widely used as heterogeneous catalysts in important reactions such as dehydrogenation and steam reforming, where the desorption of H2 molecules is one of the key steps. Herein, based on density functional theory calculations, we have simulated the temperature programmed desorption (TPD) spectra of hydrogen (H) on the Ni(100) surface using the mean-field approximation and a new HH dimer desorption method. Zero-point energy corrections are also considered. It is found that the centered-peaks of TPD obtained from simulations are in good agreement with the previous experimental results. However, the centered-peak position moves in an opposite direction to the experiments as atomic hydrogen coverage increases. We have systematically investigated the effects of the interaction between adsorbed H atoms and the diffusion of H atoms on the peak shifts, and found that they are not responsible for the experimentally observed leftward shift of the TPD peak. We then propose and confirm that the presence of subsurface H atoms plays a key role in the leftward peak shift. This work refines the interpretation of H2 TPD spectra and contributes to the understanding of microscopic behaviors of H atoms on the Ni(100) surface.

Deuterium retention and ammonia production from D-implanted 316 L stainless steel: insights for future fusion reactors

We present a systematic study that quantifies deuterium (D) retention and ammonia (ND3) production from 316 L stainless steel (SS316L) following the implantation of D ions in conditions similar to the ones expected in the ITER tokamak, i.e. with kinetic energy below 300 eV. Using Temperature Programmed Desorption (TPD) after deuterium ion implantation at 250 eV/D, we show that deuterium retention increases linearly with the D fluence up to 1021 D+m−2, with a retention probability of 18%. For higher D fluence, deuterium retention increases sub-linearly. Analysis of the TPD spectra evolution with varying storage time in vacuum after D implantation, shows that D retention is influenced by D diffusion into the bulk of SS316L. Subsequent to D ion implantation, we evidence the efficient production of ND3 molecules during TPD, between 400 K and 750 K, from the nitrogen present naturally in SS316L. Up to 21% of the D release during TPD can be found in ND3 molecules, indeed. The fraction of ND3 in the total D release depends both on the D ion fluence and the nitrogen concentration profile in the bulk. At least 7% of the D release is found in the form of ND3 molecules, even at a fluence of 2 × 1021 D+m−2 and for a natural N concentration bulk profile. Both N diffusion and D diffusion into the bulk appear to dictate the kinetics of ND3 production. Our findings of efficient production of ND3 in D-implanted austenitic 316 L stainless steel underline the need for similar studies on reduced-activation ferritic/martensitic (RAFM) steels that contain similar content of nitrogen and will be used in fusion reactor prototypes.

A Multitechnique Study of C2H4 Adsorption on Fe3O4(001).

The adsorption/desorption of ethene (C2H4), also commonly known as ethylene, on Fe3O4(001) was studied under ultrahigh vacuum conditions using temperature-programmed desorption (TPD), scanning tunneling microscopy, X-ray photoelectron spectroscopy, and density functional theory (DFT)-based computations. To interpret the TPD data, we have employed a new analysis method based on equilibrium thermodynamics. C2H4 adsorbs intact at all coverages and interacts most strongly with surface defects such as antiphase domain boundaries and Fe adatoms. On the regular surface, C2H4 binds atop surface Fe sites up to a coverage of 2 molecules per (√2 × √2)R45° unit cell, with every second Fe occupied. A desorption energy of 0.36 eV is determined by analysis of the TPD spectra at this coverage, which is approximately 0.1-0.2 eV lower than the value calculated by DFT + U with van der Waals corrections. Additional molecules are accommodated in between the Fe rows. These are stabilized by attractive interactions with the molecules adsorbed at Fe sites. The total capacity of the surface for C2H4 adsorption is found to be close to 4 molecules per (√2 × √2)R45° unit cell.

Analysis of Temperature-Programmed Desorption via Equilibrium Thermodynamics.

Temperature-programmed desorption (TPD) experiments in surface science are usually analyzed using the Polanyi-Wigner equation and/or transition-state theory. These methods are far from straightforward, and the determination of the pre-exponential factor is often problematic. We present a different method based on equilibrium thermodynamics, which builds on an approach previously used for TPD by Kreuzer et al. (Surf. Sci. 1988). Equations for the desorption rate are presented for three different types of surface-adsorbate interactions: (i) a 2D ideal hard-sphere gas with a negligible diffusion barrier, (ii) an ideal lattice gas, that is, fixed adsorption sites without interaction between the adsorbates, and (iii) a lattice gas with a distribution of (site-dependent) adsorption energies. We show that the coverage dependence of the sticking coefficient for adsorption at the desorption temperature determines whether the desorption process can be described by first- or second-order kinetics. The sticking coefficient at the desorption temperature must also be known for a quantitative determination of the adsorption energy, but it has a rather weak influence (like the pre-exponential factor in a traditional TPD analysis). Quantitative analysis is also influenced by the vibrational contributions to the energy and entropy. For the case of a single adsorption energy, we provide equations to directly convert peak temperatures into adsorption energies. These equations also provide an approximation of the desorption energy in cases that cannot be described by a fixed pre-exponential factor. For the case of a distribution of adsorption energies, the desorption spectra cannot be considered a superposition of desorption spectra corresponding to the different energies. Nevertheless, we present a method to extract the distribution of adsorption energies from TPD spectra, and we rationalize the energy resolution of TPD experiments. The analytical results are complemented by a program for simulation and analysis of TPD data.

VO Cluster-Stabilized H2O Adsorption on a TiO2 (110) Surface at Room Temperature.

We probe the adsorption of molecular H2O on a TiO2 (110)-(1 × 1) surface decorated with isolated VO clusters using ultrahigh-vacuum scanning tunneling microscopy (UHV-STM) and temperature-programmed desorption (TPD). Our STM images show that preadsorbed VO clusters on the TiO2 (110)-(1 × 1) surface induce the adsorption of H2O molecules at room temperature (RT). The adsorbed H2O molecules form strings of beads of H2O dimers bound to the 5-fold coordinated Ti atom (5c-Ti) rows and are anchored by VO. This RT adsorption is completely reversible and is unique to the VO-decorated TiO2 surface. TPD spectra reveal two new desorption states for VO stabilized H2O at 395 and 445 K, which is in sharp contrast to the desorption of water due to recombination of hydroxyl groups at 490 K from clean TiO2(110)-(1 × 1) surfaces. Density functional theory (DFT) calculations show that the binding energy of molecular H2O to the VO clusters on the TiO2 (110)-(1 × 1) surface is higher than binding to the bare surface by 0.42 eV, and the resulting H2O-VO-TiO2 (110) complex provides the anchor point for adsorption of the string of beads of H2O dimers.

Microwave N2 plasma nitridation of H-diamond (111) surface studied by ex situ XPS, HREELS, UPS, TPD, LEED and DFT

We report on an experimental investigation and density functional theory (DFT) modeling of the physico-chemical properties of nitrided diamond (111) surface prepared by exposing a hydrogenated diamond (111) surface to high purity nitrogen microwave plasma (MW(N2)). Ex-situ X-ray photoelectron spectroscopic analysis showed that the maximum nitrogen coverage is ∼1/4 monolayer alongside coadsorbed hydrogen, as corroborated by high-resolution electron energy loss spectroscopy (HREELS). The observed broad peak at ∼630 °C in the N2 temperature programmed desorption spectrum suggests that nitrogen desorption substantially occurs below 700 °C. As nitride surface exhibits an increase in electron affinity/work function compared to the hydrogenated surface. Low energy electron diffraction of the nitride surface exhibits a 1×1 pattern, which confirms that the MW(N2) exposure results in low-level damage to the diamond (111) surface; these results complement well with the presence of 1st order optical phonon peak (∼300 meV), the characteristic signature of a highly ordered diamond surface, on the HREEL spectrum. DFT simulations reveal that it is facile for nitrogen to insert into the CH bond on H-diamond (111), forming NH(ad) species adsorbed over C(111), which dimerizes into NH-NH(ad) at increasing coverages. The computed modes of vibration are in qualitative agreement with the HREELS data.

Selective adsorption of trace gaseous ammonia from air by a sulfonic acid-modified silica xerogel: Preparation, characterization and performance

The toxic and corrosive gaseous ammonia (NH3) poses serious environmental and health risks. However, removal of low concentration NH3 from air remains challenging. In this work, a SO3H-modified silica xerogel (MPTS-X) with good porous structure stability and abundant Bronsted acid sites was fabricated, and its physicochemical properties and adsorption performance for NH3 were systematically investigated. Static adsorption experiments showed the MPTS-1.0 had high NH3 adsorption capacity of 4.02 mmol⋅g−1 at 0.1 bar and 7.00 mmol⋅g−1 at 1.0 bar, which was much higher than that of MPTS-0 (3.19 and 1.95 mmol⋅g−1). Langmuir-Freundlich isotherm model fitted the experimental data of NH3 adsorption well, implying that the MPTS-1.0 surface is not homogeneous and there are different adsorption sites, which was further confirmed by temperature programmed desorption spectrum analysis. According to IAST calculation, the adsorption selectivity of MPTS-1.0 for NH3/N2 (1: 9) and NH3/CO2 (1: 1) was 6175 and 165 at 1.0 bar, respectively, indicating the MPTS-1.0 has excellent adsorption selectivity. Dynamic adsorption experiments and field test demonstrated the MPTS-1.0 could quickly capture trace NH3, even if the initial concentration is as low as 2 ppm. Successive adsorption–desorption experiments demonstrated the MPTS-1.0 had good regenerability. In-situ infrared spectroscopy analyses indicated NH3 adsorption on the MPTS-1.0 was mainly due to hydrogen bonding interaction and proton transfer to form Si-OH…NH3 and -SO3-NH4+, respectively. NH3 molecules bound firmly to acidic sites on the xerogel surface, which reduced re-release risk. This work may provide a feasible way to develop promising adsorbents for the removal of gaseous ammonia from air.

Hydrogen storage in TiVCrMo and TiZrNbHf multiprinciple-element alloys and their catalytic effect upon hydrogen storage in Mg

Hydrogen storage performance of nearly equimolar alloys TiVCrMo and TiZrNbH (HEA's) was studied. The alloys were prepared by repeated arc-melting in the form of single-phase alloys and as their multi-phase analogues prepared either by high-energy ball milling (HEBM) of the arc-melted ingots or by HEBM of pure elements. Besides these four-component experimental materials, also their mixtures with Mg were investigated that were prepared by HEBM with Mg (composition in both cases was Mg – 10 wt % HEA). Hydrogen sorption experiments were carried out in temperature interval between 240 °C and 380 °C under hydrogen-gas pressure up to 50 bars. Kinetic curves, temperature-programmed desorption spectra and concentration-pressure isotherms were measured. It was found that activation energy of hydrogen desorption, |Ea|, for materials with Mg was significantly decreased compared to pure Mg. Hydride formation enthalpy, ΔH, observed for all the materials under study was about the same as that for pure MgH2. Hydrogen absorption capacity in pure four-component HEA's was negligible; only hydrogen surface adsorption was detected. The capacity of mixtures of HEA's with Mg was between 3.5 and 6 wt % H2.

The Thermodesorption of CO from the Mo(110) Surface

The problem of the CO adsorption and dissociation on the Mo(110) surface has been studied by means of temperature-programmeddesorption (TPD) and density-functional (DFT) calculations. The TPD spectra show a first-order CO desorption, which indicates thedesorption from a virgin state, not a recombinative form of desorption. The height of the potential barrier for CO dissociation (2.75 eV), estimated from DFT calculations, substantially exceeds the energy of CO chemisorption on the Mo(110) surface (2.1 eV), which refutes a thermally induced CO dissociation. Monte Carlo simulations of TPD spectra, performed with the use of estimated chemisorption energies, are in good agreement with experiment and demonstrate that the two-peak shape of the spectra can be explained without involving the CO dissociation.

Same-Energy UV Photons and Low-Energy Electrons Activating Methane and Ammonia Frozen in Amorphous Solid Water.

UV photons and low-energy electrons play an important role in the evolution of various molecules in the interstellar medium (ISM). Here, we examined the product molecule formation as a result of irradiation of 193 nm photons and 6.4 eV electrons (same energy under identical laboratory conditions) on D2O|CH4 + ND3|D2O sandwiched films deposited on Ru(0001) substrate at 25 K in ultrahigh vacuum as a model for processes in the ISM. Temperature-programmed desorption spectra performed following the irradiation revealed the signature of hydrazine and formamide product molecules. These molecules were, however, formed exclusively following the photons' irradiation. These results were compared with the products obtained from a D2O|CH4|D2O sample without ammonia, where deuterated formaldehyde was the dominant product, formed also by photons only. Our results indicate that the photon-induced activation of the cofrozen molecules within D2O occurs via direct (partial) dissociation of the host and embedded molecules, followed by sample annealing. The electron-induced activation occurs through a direct dissociative electron attachment mechanism. The results presented here suggest possible pathways to generate various C-N, C-O, C-C, N-O, and N-H bonds containing molecules in the ISM.

Double-Phase Heterostructure within Fe-Doped Cu2–xS Quantum Dots with Boosted Electrocatalytic Nitrogen Reduction

Electrochemical nitrogen reduction reaction (NRR) is considered as one of the most promising methods for NH₃ synthesis under room temperature and ambient pressure. A grand challenge of NRR is the development of efficient electrocatalysts, for which the delicate nanostructuring of catalysts plays an important role. Herein, a series of Fe-doped Cu₂–ₓS quantum dots (QDs) are synthesized with multiple active sites and interface engineering, in which the double-phase heterostructure plays a key role for boosting NRR activity. The yield of NH₃ was obviously improved with the increase of Fe content from 0 to 3% but started to decrease with Fe from 3 to 9%. The optimized Fe₃%–Cu₂–ₓS QDs show an outstanding NH₃ yield of 26.4 μg h–¹ mg–¹cₐₜ at −0.7 V (vs the reversible hydrogen electrode), which is 5 times higher than that of Cu₂–ₓS QDs. More importantly, we observed that the highest NRR activity in Fe₃%–Cu₂–ₓS QDs was ascribed to the formation of an inherent double-phase heterostructure of Cu₂–ₓS/Cu₅FeS₄, whereas the complete conversion to single-phase Cu₅FeS₄ with increased Fe doping (9%) resulted in the activity decrease. Further, N₂ temperature-programmed desorption and electrochemical impedance spectra characterizations confirm the stronger chemical adsorption of N₂ and faster charge transfer in the Cu₂–ₓS/Cu₅FeS₄ QDs. A plausible mechanism was proposed for the double-phase Cu₂–ₓS/Cu₅FeS₄ heterostructure, where the interface provides efficient charge transfer and more active sites of Cu, Fe, and S for the synergetic adsorption and activation of N₂. Our work provides a simple strategy for the design of NRR electrocatalysts, which may also bring new inspiration for the preparation of the inherent double-phase heterostructure within other doped QDs.

Observation of Molecular Hydrogen Produced from Bridging Hydroxyls on Anatase TiO2(101).

Anatase TiO2 is used extensively in a wide range of catalytic and photocatalytic processes and is a promising catalyst for hydrogen production. Here, we show that molecular hydrogen was produced from bridging hydroxyls (HOb) on the (101) surface of single-crystal anatase (TiO2(101)). This stands in contrast to rutile TiO2(110), where HOb pairs react to form H2O. Electron bombardment at 30 K produced bridging oxygen vacancies in the surface. Deuterated bridging hydroxyls (DOb) were subsequently formed via dissociation of adsorbed D2O and confirmed by infrared reflection-absorption spectroscopy. During temperature-programmed desorption (TPD) spectroscopy, D2 desorption was observed at 520 K. Density functional theory calculations show that both H2 and H2O production from HOb are endothermic at 0 K on TiO2(101), but H2 (H2O) desorption is entropically driven above 230 K (800 K). The calculated activation barrier for H2 desorption is 1.40 eV, which is similar to the desorption energy obtained from analysis of the D2 TPD spectra. The H2 desorption likely proceeds in two steps: H atom diffusion on the surface and then recombination.

Coexistence of first-order and second-order desorption processes during temperature-programmed desorption of Bi on Ni(100) analyzed by kinetic Monte Carlo techniques

The application of temperature-programmed desorption (TPD) techniques in heterogeneous catalysis to probe, among other things, the nature of the reactions on the surface solid catalyst, and ultimately, the kinetics of desorbed species, is hampered by the inability to make direct observations of adsorbates when they are most catalytically active. Thus, it is almost impossible to make a direct association between a given elementary surface process and a key feature on the TPD spectra, such as the nature and number of peaks. What kinetic Monte Carlo simulations have shown, on the other hand, is that the complex surface evolution during TPD is controlled effectively by just a few parameters that relate to the surface kinetics and energetics. In this study, we will use kinetic Monte Carlo approach to show that double-peaked TPD spectra obtained from adsorption of Bi adsorbates on Ni(100) at an initial temperature of 800 K and subsequent TPD runs for high preadsorbed coverages can indeed be explained satisfactorily by assuming predominant first-order desorption kinetics coupled with adsorbate-adsorbate lateral interactions, in agreement with prior studies. While not totally discounting the presence of Bi dimers, and thus second-order desorption, our study is sensitive enough to reveal the extent of their presence. In other words, we propose that dimers can coexist with Bi adatoms in small amounts while retaining the key features of the TPD spectra, provided the kinetic parameters associated with dimer formation (and dissolution) are well within a certain range. On the other hand, any model in which dimers are present to a degree in which they are not totally dominated by adatoms cannot produce TPD spectra that are consistent with the experiment.

Chirality detection of surface desorption products using photoelectron circular dichroism.

Chirality detection of gas-phase molecules at low concentrations is challenging as the molecular number density is usually too low to perform conventional circular dichroism absorption experiments. In recent years, new spectroscopic methods have been developed to detect chirality in the gas phase. In particular, the angular distribution of photoelectrons after multiphoton laser ionization of chiral molecules using circularly polarized light is highly sensitive to the enantiomeric form of the ionized molecule [multiphoton photoelectron circular dichroism (MP-PECD)]. In this paper, we employ the MP-PECD as an analytic tool for chirality detection of the bicyclic monoterpene fenchone desorbing from a Ag(111) crystal. We record velocity-resolved kinetics of fenchone desorption on Ag(111) using pulsed molecular beams with ion imaging techniques. In addition, we measure temperature-programmed desorption spectra of the same system. Both experiments indicate weak physisorption of fenchone on Ag(111). We combine both experimental techniques with enantiomer-specific detection by recording MP-PECD of desorbing molecules using photoelectron imaging spectroscopy. We can clearly assign the enantiomeric form of the desorption product fenchone in sub-monolayer concentration. The experiment demonstrates the combination of MP-PECD with surface science experiments, paving the way for enantiomer-specific detection of surface reaction products on heterogeneous catalysts for asymmetric synthesis.

Nitrogen bonding, work function and thermal stability of nitrided graphite surface: An in situ XPS, UPS and HREELS study

In this study, we investigate the chemical and electronic properties of nitrogen incorporated highly oriented pyrolytic graphite (N–HOPG) surface. The N–HOPG surfaces were prepared by three methods: radio frequency N2 (RF(N2)) plasma, microwave N2 (MW(N2)) plasma and N2+ ion implantation. The surface chemical states of carbon–nitrogen bonds on the N–HOPG surfaces, evolution of defects and thermal stability were investigated by X-ray photoelectron spectroscopy, high-resolution electron energy loss spectroscopy (HREELS) and ultraviolet photoelectron spectroscopy. Nitrogen exists in graphitic–N bonding state predominantly on the low damage N–HOPG surfaces (RF(N2) plasma at 9.3 Pa and 200 eV N2+ ion implantation) and in pyridine–N bonding state on high damage N–HOPG surfaces (RF(N2) plasma at 4.0 Pa and 500 eV N2+ ion implantation). Partial structural recovery is possible for low damage N–HOPG surfaces upon annealing. HREELS analysis revealed preferential bonding of hydrogen to defect sites and retention of graphite lattice structure for N–HOPG surfaces with low-level of surface damage. Furthermore, low damage N–HOPG surfaces exhibited low work function due to incorporation of nitrogen at graphitic sites. HCN temperature programmed desorption spectra showed a broad peak positioned at 550 °C which is associated with desorption of pyrrolic–N content.

Simulated temperature programmed desorption experiments for nanoceria powders

Density functional theory calculations (DFT), coupled with microkinetic modelling, have been used to simulate Temperature Programmed Desorption (TPD) experiments for calcined ceria nanopowders with the aim to gain insight into the chemistry governing their high redox activity. Our simulations consider two main nanoparticle models. One is a perfect ceria octahedron supercharged with adsorbed oxygen molecules turned into superoxide ions, as has previously been used to explain the enhanced oxygen storage capacity (OSC) in nanoceria. The other model is a variant where we have introduced oxygen vacancies under ridge Ce ions, thereby reducing their coordination numbers to five. The results from our microkinetic modelling suggest that including such five-coordinated Ce adsorption sites results in a TPD spectrum that better matches the experimental counterpart in terms of both peak position and width. In addition, this new structural model allows for the co-existence of Ce3+ ions, superoxide ions and O2 molecules, as seen in experiments in the literature.

Formic acid adsorption and decomposition on clean and atomic oxygen pre-covered Cu(100) surfaces.

Formic acid adsorption and decomposition on clean Cu(100) and two atomic oxygen pre-covered Cu(100) surfaces have been studied using surface science techniques including scanning tunneling microscopy, low-energy electron diffraction, x-ray photoelectron spectroscopy, and infrared reflection-absorption spectroscopy. The two atomic oxygen pre-covered Cu(100) surfaces include an O-(22 ×2)R45° Cu(100) surface and an oxygen modified Cu(100) surface with a local O-c(2 × 2) structure. The results show that the O-(22 ×2)R45° Cu(100) surface is inert to the formic acid adsorption at 300 K. After exposing to formic acid at 300 K, bidentate formate formed on the clean Cu(100) and local O-c(2 × 2) area of the oxygen modified Cu(100) surface. However, their adsorption geometries are different, being vertical to the surface plane on the former surface and inclined with respect to the surface normal with an ordered structure on the latter surface. The temperature programmed desorption spectra indicate that the formate species adsorbed on the clean Cu(100) surface decomposes into H2 and CO2 when the sample temperature is higher than 390 K. Differently, the proton from scission of the C-H bond of formate reacts with the surface oxygen, forming H2O on the oxygen modified Cu(100) surface. The CO2 signal starts increasing at about 370 K, which is lower than that on clean Cu(100), indicating that the surface oxygen affiliates formate decomposition. Combining all these results, we conclude that the surface oxygen plays a crucial role in formic acid adsorption and formate decomposition.

Theoretical Parameter-Free Analysis Model for Temperature-Programmed Desorption (TPD) Spectra.

This paper proposes a parameter-free mathematical model of analyzing either monosite or multisite temperature-programmed desorption (TPD) spectra. By linearizing the integral function difference, the desorption kinetic parameters, such as the desorption order n, the desorption activation energy Ed, and the pre-exponential factor ν, can be extracted simultaneously with promising accuracy. A custom “ant” is further established in the model to explore the spectra by a “prediction–correction” loop, and the kinetics and the coverage distribution of the individual peak in the spectra can be solved sequentially. Meanwhile, eight cases on spectrum analysis, including but not limited to the spectrum with coverage-dependent kinetics, the spectrum affected by the noise, the practical spectrum, are demonstrated to fully understand the model’s principle, process, and application. Moreover, the model optimization and resolution limitation are further discussed to stimulate the future potential of the innovative parameter-free model.