Surface Active Oxygen Species Research Articles

Ultrasensitive Detection of Dimethylamine Gas for Early Diagnosis of Parkinson's Disease Using CeO2-Coated Ti3C2Tx MXene/Carbon Nanofibers.

Parkinson's disease is a prevalent neurological disorder, with dimethylamine (DMA) recognized as a crucial breath biomarker, particularly at the parts per billion (ppb) level. Detecting DMA gas at this level, especially at room temperature and high humidity, remains a formidable challenge. This study presents an ultrasensitive chemiresistor DMA gas sensor, leveraging the CeO2-coated Ti3C2Tx MXene/carbon nanofiber (CeO2/MXene/C NFs) heterostructure to enhance dimethylamine sensing. The high conductivity of MXene, combined with C-Ti-O bonds and a sp2 hybridized hexagonal carbon structure, increases surface active sites. The presence of Ce3+ promotes the formation of surface-active oxygen species, while the MXene-CeO2 heterojunction broadens the electron depletion layer. Theoretical calculations reveal that the highest adsorption energy for DMA gas is at the Ce top site, explaining the sensor's satisfactory sensitivity, rapid response and recovery process, low detection limit (5 ppb), and high selectivity at room temperature. The Ce3+/Ce4+ dynamic self-refresh mechanism, involving surface hydroxyl elimination, enhances the sensor's performance under high-humid conditions. Clinical breath tests demonstrate the sensor's ability to distinguish between healthy individuals and Parkinson's disease patients, paving the way for developing next-generation sensors for early diagnosis of neurological disorders.

Supported Co3O4 catalyst on modified UiO-66 by Ce4+ for completely catalytic oxidation of toluene

Creating a new low-temperature catalyst in decreasing the emission of volatile organic compounds (VOCs) has great significance under different industrial production situations. In particular, the Zr-UiO-66 is optimized by different amounts of cerium, which not only enhances the physicochemical stability but also increases the number of active sites of CexZryUiO-66. Furthermore, the catalysts with Co3O4 nanoparticles supported on CexZryUiO-66 were successfully prepared via impregnation method. In the process of toluene degradation, the Co/Ce1Zr2-UiO-66 attains a 90% conversion rate at 210 °C with a space velocity of 60000 mL/(g·h) and toluene concentration at 1000×10–6. Meanwhile, the carbon dioxide selectivity reaches 100% at 218 °C. The Co/Ce1Zr2-UiO-66 shows great water resistance (3 vol% H2O). Multiple characterization methods were used to figure out the physicochemical properties of the catalysts. It is found that the addition of an appropriate amount of cerium can enhance stability of UiO-66 and surface lattice oxygen proportion. Additionally, the stronger electron transfer between Ce4+ and Co2+ enables the Co/Ce1Zr2-UiO-66 to possess more active surface oxygen species and Co3+ cationic species in all samples.

Three-dimensionally ordered macroporous CeZrVOx catalyst with remarkable NH3-SCR performance and SO2 tolerance: Key roles of the morphology and highly dispersed V species

Developing effective low-temperature deNOx catalysts with high activity, SO2 tolerance, and stability is crucial yet challenging. Thus, in this work, CeZrVOx catalyst with a three-dimensional ordered macroporous structure was successfully prepared using the PMMA hard template method, and the catalyst has a macropore diameter of up to 110−140 nm. The modification with highly dispersed V significantly enhances the low-temperature activity and broadens the activity temperature window of the catalyst. This is mainly attributed to the increased number of surface acid sites, as well as the higher proportion of Ce3+ and active surface oxygen species induced by V modification. The V species prepared by this method are highly dispersed on the CeZrOx solid solution and combine with Ce to form CeVO4, which is also an important factor in enhancing catalytic activity. The catalyst does not react with SO2 to produce inactive sulfate species; even the formed cerium sulfate species are beneficial for high-temperature performance. More importantly, due to its unique interconnected three-dimensional ordered structure, the catalyst can significantly inhibit the blockage and coverage of NH4HSO4 on the catalyst, thereby exhibiting remarkable resistance to physical poisoning caused by SO2. Even in high concentrations of sulfur-containing atmospheres, the catalyst still shows high catalytic activity. This work offers meaningful guidance into developing denitration catalysts that show superior performance and robust resistance to both physical and chemical poisoning induced by SO2.

The effect of Fe2O3 doping on a Pt/Co3O4 catalyst for CO oxidation: Improvement of thermal stability and catalytic activity

Although Pt/Co3O4 is an active catalyst for CO oxidation, its low thermal stability may impede its application. The thermal stability and catalytic performance of Pt/Co3O4 were considerably enhanced by Fe2O3 doping. Fe2O3 doping stabilized the mesostructured material during the high-temperature treatment, and the Fe2O3-doped samples retained a larger specific surface area. The characterization results revealed that Fe2O3 doping inhibited catalyst crystallization and decomposition and the growth of catalyst grains during high-temperature calcination. The Fe2O3 doping reduced the Co-O bond strength in the surface Co3O4 lattice, increased the Co3+ ratio, and generated highly active surface oxygen species. Fe2O3 doping also facilitates CO2 desorption, which improves CO adsorption and oxidation. SO2 and NO impede CO oxidation on Pt/Fe2O3/Co3O4. This negative impact was caused by the inert species formed when SO2 or NO reacted with O2 on the catalyst, such as SO42-, HSO4-, or nitrate species, which covered the active sites.

The influence of crystal facet on the catalytic performance of MOFs-derived NiO with different morphologies for the total oxidation of propane: The defect engineering dominated by solvent regulation effect

Crystal facet and defect engineering are crucial for designing heterogeneous catalysts. In this study, different solvents were utilized to generate NiO with distinct shapes (hexagonal layers, rods, and spheres) using nickel-based metal-organic frameworks (MOFs) as precursors. It was shown that the exposed crystal facets of NiO with different morphologies differed from each other. Various characterization techniques and density functional theory (DFT) calculations revealed that hexagonal-layered NiO (NiO-L) possessed excellent low-temperature reducibility and oxygen migration ability. The (111) crystal plane of NiO-L contained more lattice defects and oxygen vacancies, resulting in enhanced propane oxidation due to its highest O2 adsorption energy. Furthermore, the higher the surface active oxygen species and surface oxygen vacancy concentrations, the lower the C−H activation energy of the NiO catalyst and hence the better the catalytic activity for the oxidation of propane. Consequently, NiO-L exhibited remarkable catalytic activity and good stability for propane oxidation. This study provided a simple strategy for controlling NiO crystal facets, and demonstrated that the oxygen defects could be more easily formed on NiO(111) facets, thus would be beneficial for the activation of C−H bonds in propane. In addition, the results of this work can be extended to the other fields, such as propane oxidation to propene, fuel cells, and photocatalysis.

Amorphous Ce-Ti composite as an efficient bifunctional catalyst for deep oxidation of volatile organic compounds and selective catalytic reduction of NO

In this work, a series of Ce-Ti composite oxides with different Ti/Ce molar ratios was prepared by co-precipitation method, and investigated for the catalytic degradation of toluene and selective catalytic reduction of NO. The phase transition process between Ce species and Ti species is limited by modulating the interaction between Ce4+ and Ti4+, while a completely amorphous composite is generated with an appropriate molar ratio of Ti/Ce (1.5/1). The catalyst CeTi1.5Ox exhibits the best catalytic performance, where the values of T90 and T50 for deep degradation of toluene are 297 and 330 °C respectively at high weight hours space velocity (WHSV=120000 mL/(g⋅h)). Compared with CeO2, T90 and T50 decrease by 48 and 34 °C respectively while declining by 67 and 70 °C compared to TiO2. For the SCR reaction, CeTi1.5Ox reaches 100% NO conversion at 250 °C with WHSV=60000 mL/(g⋅h), reduced by 50 °C compared to pure CeO2. The amorphous nanostructure with highly dispersed Ce and Ti species was confirmed by transmission electron microscopy (TEM) and X-ray diffraction (XRD) characterizations. The X-ray photoelectron spectroscopy (XPS) and Raman analyses show that a large number of active Ce-O-Ti species and surface oxygen vacancies are generated due to the strong interaction between Ti4+ and Ce4+ in CeTi1.5Ox. Additionally, H2-TPR and O2-TPD further confirm that the interaction promotes the low-temperature reducibility and mobility of surface-active oxygen species. Meanwhile, in-situ DRIFTS study reveals that CeTi1.5Ox with amorphous nanostructure can dramatically enhance the dissociative and complete oxidation capacity for toluene.

Photocatalytic toluene oxidation with nickel-mediated cascaded active units over Ni/Bi2WO6 monolayers

Adsorption and activation of C–H bonds by photocatalysts are crucial for the efficient conversion of C–H bonds to produce high-value chemicals. Nevertheless, the delivery of surface-active oxygen species for C–H bond oxygenation inevitably needs to overcome obstacles due to the separated active centers, which suppresses the catalytic efficiency. Herein, Ni dopants are introduced into a monolayer Bi2WO6 to create cascaded active units consisting of unsaturated W atoms and Bi/O frustrated Lewis pairs. Experimental characterizations and density functional theory calculations reveal that these special sites can establish an efficient and controllable C–H bond oxidation process. The activated oxygen species on unsaturated W are readily transferred to the Bi/O sites for C–H bond oxygenation. The catalyst with a Ni mass fraction of 1.8% exhibits excellent toluene conversion rates and high selectivity towards benzaldehyde. This study presents a fascinating strategy for toluene oxidation through the design of efficient cascaded active units.

Engineering binary CrmNb1-mOx (m = 0.1, 0.3, 0.5) oxides catalysts to enhance its NH3-SCR denitration activity and SO2 resistance: Study on the influence of redox property and acidity

It is still a challenge to create novel simply environmentally friendly NH3-SCR denitration catalysts in presence of SO2 and H2O, and to further understand the role of redox property and acidity of catalyst. In this work, a series of binary CrmNb1-mOx (m = 0.1, 0.3 and 0.5) oxides with different Cr/Nb ratio were engineered for NH3-SCR denitration by using the citric acid complex method. Among these catalysts, Cr0.3Nb0.7Ox revealed best catalytic performance with over 90 % NO conversion in the range of 210–390 ℃ and great SO2 and H2O resistance. The effects of different Cr/Nb ratio on catalytic activity was investigated though following characterization such as Raman spectroscopy, Transmission electron microscopy (TEM), X-ray powder diffraction (XRD), N2 physical adsorption, NO-Temperature programmed desorption (NO-TPD), H2-Temperature program reduction (H2-TPR), X-ray photoelectron spectra (XPS), NH3-Temperature programmed desorption (NH3-TPD) and In situ Diffuse reflectance infrared Fourier transform spectroscopy (In situ DRIFTS). The impact of surface redox property and acidity on catalytic performance was further investigated by changing the Cr/Nb ratio. The results suggest that different Cr/Nb ratio result in catalysts having different Brunauer-Emmett-Teller (BET) surface area, and variation of crystal structure, generating the improvement of the surface acid amount and the enhancement of the oxidizing ability due to existence of more surface active oxygen species. Besides, the results of in situ DRIFTS verify that more acid sites are exposed on the Cr0.3Nb0.7Ox surface and react with absorbed NOx even in the existence of SO2, which followed Langmuir-Hinshelwood (L-H) mechanism.

Unravelling the synergistic effects in GdCe composite oxides supported biochar catalysts for formaldehyde elimination: Elevated performance and SO2 toleration

A chain of GdCe oxides boosted biochars derived from maize straw and sewage sludge (GdyCe1-y/MPBs) were fabricated for formaldehyde (HCHO) catalytic decomposition. The ingenerate relationship between the abatement performance and corresponding structural feature was comprehensively evaluated by XPS, in situ DRIFTS, BET, XRD, SEM and H2-TPR. Meanwhile, 10%Gd0.25Ce0.75/MPB exhibited excellent performance, favorable SO2 and moisture toleration over a broad temperature range from 160 to 320 ℃, where it achieved 96.8% removal efficiency with 90.5 % selectivity at 200 ℃. The single or united effects of O2, SO2, H2O on HCHO abatement over 10 %Gd0.25Ce0.75/MPB were tested, and the findings demonstrated that the suppressive effects of SO2 and H2O outweighed the promoting influence of O2 within a specific range. Gd and Ce co-modified MPB revealed superior HCHO removal capability in contrast to that of Gd or Ce severally modified MPB, ascribing to the synergistic effect of GdOx and CeOx and benefitting from the augmentation of surface area and total pore volume, the aggrandizement of surface active oxygen species, the promotion of redox ability and the inhibition crystallization of CeOx. According to in situ DRIFTS, a series of intermediates including formate species and dioxymethylene (DOM) were produced, which would eventually decompose into H2O and CO2. In addition, the mass transfer and diffusion of the reactants along with the accessibility of the catalytic sites were enlarged by the hierarchical porous structure of the support, which were also answerable for its distinguished catalytic performance. Furthermore, 10%Gd0.25Ce0.75/MPB possessed remarkable potential for industrial applications.

Investigation of catalytic methane oxidation over Ag/Co2MOx (M = Co, Ni, Cu) catalysts with varying interfacial electron transfer

Atom-doped Co3O4 catalysts loaded with Ag were examined as cost-effective catalysts for methane oxidation. The synthesized Ag/Co2NiOx catalysts exhibited distinctive surface characteristics in contrast with Ag/Co3O4 and Ag/Co2CuOx catalysts prepared using a similar method. Characterization results unveiled that Ag/Co2NiOx featured a higher presence of active surface oxygen species, lattice defects, a larger surface area, and enhanced reducibility. A methane oxidation catalytic performance followed the sequence: Ag/Co2NiOx > Ag/Co3O4 > Ag/Co2CuOx. The investigation delved into methane degradation pathways on the surfaces of three catalysts, examining their behavior under both aerobic and anaerobic atmospheres through in-situ DRIFTS analysis. Furthermore, introducing Ag showed a marked positive effect on Co-Ni mixed oxide, inducing electron transfer and a more active electron system, whereas it exhibited an inverse impact within the surface of Co-Cu mixed oxide. This work provides innovative perspectives on the development of forthcoming environmental catalysts.

High-temperature calcination dramatically promotes the activity of Cs/Co/Ce-Sn catalyst for soot oxidation

Catalytic oxidation of soot is of great importance for emission control on diesel vehicles. In this work, a highly active Cs/Co/Ce-Sn catalyst was investigated for soot oxidation, and it was unexpectedly found that high-temperature calcination greatly improved the activity of the catalyst. When the calcination temperature was increased from 500 °C to 750 °C, T50 decreased from 456.9 °C to 389.8 °C in a NO/O2/H2O/N2 atmosphere. Characterization results revealed that high-temperature calcination can promote the ability to transfer negative charge density from Cs to other metal cations in Cs/Co/Ce-Sn, which will facilitate the production of more oxygen defects and the generation of more surface-active oxygen species. Surface-active oxygen species are beneficial to the oxidation of NO to NO2, leading to the high yield of NO2 exploitation. Therefore, the Cs/Co/Ce-Sn catalyst calcined at 750 °C demonstrated higher activity than that calcined at 500 °C. This work provides a pathway to prepare high efficiency catalysts for the removal of soot and significant insight into the effects of calcination on soot oxidation catalysts.

Effect of Interaction between Pt and Different Crystalline Phases of TiO2 on Benzene Oxidation

To evaluate the effects of different TiO2 crystalline phases on the catalytic oxidation performance of benzene on Pt-loaded TiO2 catalysts, physicochemical examinations were conducted using several spectroscopic and analytical techniques. Obvious effects on the valence state and morphology of Pt were exhibited by different crystalline phases. The rutile phase favored the formation of specific Pt(111) crystal faces, which enhanced the amount of surface-active oxygen species. Moreover, the àPt-O-Ti species was formed between Pt4+ and Ti at the edge of the Pt nanoparticles, promoting both electron flow and the transfer of reactive oxygen species, thus accounting for catalytic activity.

Catalytic oxidation of formaldehyde by MnOx-decorated anatase TiO2{001}: Investigation of the effect of calcination temperature on catalytic activity and reaction mechanism

The removal of indoor formaldehyde (HCHO) is crucial for human health. The design of highly catalytically active nonprecious metal catalysts has major challenges, and the use of transition metal element modification to improve the catalytic performance is an effective strategy. In this study, the active component Mn was loaded on highly active crystalline anatase TiO2{001}, and the effect of the calcination temperature on the catalytic activity was investigated. The important influence of temperature on the catalyst valence distribution, surface active oxygen species, and content was thoroughly determined by characterization techniques, such as XPS, H2-TPR, and O2-TPD. The catalytic reaction process was further analyzed by in situ infrared technology to determine the reaction intermediates and to clarify the catalyst reaction poisoning mechanism; additionally, a reasonable HCHO catalytic reaction pathway was proposed with the combination of density function theory calculations. In addition, oxygen defects on the catalyst surface were determined by EPR, and based on theoretical calculations, the oxygen defects could further reduce the reaction energy barrier through the Langmuir-Hinshelwood mechanism. By exposing specific crystal surfaces and increasing the number of oxygen defects, the catalytic activity could be effectively improved; based on these results, our study provides a concept for the subsequent development of nonprecious metal catalysts.

MOF-derived FeOx with highly dispersed active sites as an efficient catalyst for enchaning catalytic oxidation of VOCs

Highly efficient and stable catalysts serve as the crucial factor in VOCs catalytic oxidation technology. Iron-based materials are recognized as potential VOCs catalysts due to their cost-effectiveness and non-toxic nature. However, the limited catalytic performance of traditional iron oxide catalysts hinders their further industrial applications. A series of FeOx catalysts were synthesized via pyrolysis of Fe-based MOFs with diverse morphologies for toluene catalytic oxidation. Characterization results demonstrated that the FeOx-100 catalyst performed optimal characteristics, including the abundant specific surface area and smaller crystallite size, which offered highly dispersed active sites and defects for toluene oxidation. The catalytic activity of FeOx-100 was improved by adjusting the precursors and pyrolysis conditions, achieving a 50% toluene conversion at 223 °C and 90% conversion at 249 °C. The redox abilities of FeOx catalysts were carefully evaluated to assess their impact on catalytic activity. The results confirmed that FeOx-100 exhibited superior low-temperature reducibility, remarkable presence of surface active oxygen and lattice oxygen species, jointly facilitating the toluene oxidation performance at lower temperatures. The results of in situ DRIFTS provided evidence supporting a degradation pathway for toluene, likely proceeding as follows: toluene→ benzaldehyde→ benzoate→ anhydride → …→ CO2 and H2O.

Exploring the role of oxygen species on β- and γ-MnO2 catalyst under in-plasma catalysis configuration at different temperature in CO oxidation using operando TPR-DRIFTS-MS

Catalyst surface active oxygen species have an important influence on plasma catalytic oxidation. However, the reaction process of CO and O3 migration and transformation on the catalyst surface during discharge at different temperature is still unclear. In this study, β- and γ-MnO2 are selected to unveil the roles of different oxygen species under in-plasma catalysis configuration at different temperature in CO oxidation. Operando TPR-DRIFTS-MS is used to reveal CO and O3 oxidation pathways. The results show that O3 can react with CO at room temperature, and O3 is also converted to other reactive oxygen species on the catalyst surface. As the temperature increases, the oxygen species of the catalyst itself (MnO and Mn-O-Mn) can react with CO to form oxygen vacancies (Mn-□-Mn and Mn=□). Mn-□-Mn are beneficial for O2 decomposition and promotes the regeneration of MnO and Mn-O-Mn. The carbonate covered on the surface of the catalyst is the rate-determining step of CO oxidation. It is hoped that Mn-based catalysts with more reactive oxygen species and oxygen defects will be prepared to facilitate low-temperature CO oxidation under plasma conditions.

Ca and Sr co-doping induced oxygen vacancies in 3DOM La2−xSrxCe2−yCayO7−δ catalysts for boosting low-temperature oxidative coupling of methane

It is urgent to develop catalysts with application potential for oxidative coupling of methane (OCM) at relatively lower temperature. Herein, three-dimensional ordered macroporous (3DOM) La2−xSrxCe2−yCayO7−δ (A2B2O7-type) catalysts with disordered defective cubic fluorite phased structure were successfully prepared by a colloidal crystal template method. 3DOM structure promotes the accessibility of the gaseous reactants (O2 and CH4) to the active sites. The co-doping of Ca and Sr ions in La2−xSrxCe2−yCayO7−δ catalysts improved the formation of oxygen vacancies, thereby leading to increased density of surface-active oxygen species (O2−) for the activation of CH4 and the formation of C2 products (C2H6 and C2H4). 3DOM La2−xSrxCe2−yCayO7−δ catalysts exhibit high catalytic activity for OCM at low temperature. 3DOM La1.7Sr0.3Ce1.7Ca0.3O7−δ catalyst with the highest density of O2− species exhibited the highest catalytic activity for low-temperature OCM, i.e., its CH4 conversion, selectivity and yield of C2 products at 650 °C are 32.2%, 66.1% and 21.3%, respectively. The mechanism was proposed that the increase in surface oxygen vacancies induced by the co-doping of Ca and Sr ions boosts the key step of CH bond breaking and CC bond coupling in catalyzing low-temperature OCM. It is meaningful for the development of the low-temperature and high-efficient catalysts for OCM reaction in practical application.

Hydroxy and surface oxygen effects on 5-hydroxymethylfurfural oxidation to 2,5-furandicarboxylic acid on β-MnO2: DFT, microkinetic and experiment studies.

Manganese dioxide, β-MnO2, has shown potential in catalyzing the oxidation of 5-hydroxymethylfurfural (HMF) to 2,5-furandicarboxylic acid (FDCA), a monomer of bioplastic polyethylene furanoate (PEF). Herein, the insight into the hydroxy (OH) and surface oxygen effects on the HMF-to-FDCA reaction over β-MnO2 is clarified through a comprehensive investigation using density functional theory (DFT) calculations, microkinetic modeling, and experiment. Theoretical analyses revealed that both active surface oxygen and OH species (from either base or solvent) facilitate C-H bond breaking and OH insertion, promoting the catalytic activity of β-MnO2. Microkinetic modeling demonstrated that the FFCA-to-FDCA and DFF-to-FFCA steps are the rate-limiting steps of the hydroxylated and non-hydroxylated surfaces, respectively. These theoretical results agree well with the experiment when water and dimethyl sulfoxide (DMSO) were used as solvents. In addition, the synthesized β-MnO2 catalyst showed high stability and activity, maintaining stable HMF conversion (≥99 mol%) and high FDCA yield (85-92 mol%) during continuous flow oxidation for 72 hours at pO2 of 1 MPa, 393 K and LHSV of 1 h-1. Thus, considering both hydroxy and surface oxygen species is a new strategy for enhancing the catalytic activity of Mn oxides and other metal oxide catalysts for the HMF-to-FDCA reaction.

Doping SnO2 with metal ions of varying valence states: discerning the importance of active surface oxygen species vs. acid sites for C3H8 and CO oxidation.

To elucidate the valence state effect of doping cations, Li+, Mg2+, Cr3+, Zr4+ and Nb5+ with radii similar to Sn4+ (CN = 6) were chosen to dope tetragonal SnO2. Cr3+, Zr4+ and Nb5+ can enter the SnO2 lattice to produce solid solutions, thus creating more surface defects. However, Li+ and Mg2+ can only stay on the SnO2 surface as nitrates, thus suppressing the surface defects. The rich surface defects facilitate the generation of active O2-/Oδ- and acid sites on the solid solution catalysts, hence improving the reactivity. On the solid solution catalysts active for propane combustion, several reactive intermediates can be formed, but are negligible on those with low activity. It is confirmed that for propane combustion, surface acid sites play a more vital role than active oxygen sites. Nevertheless, for CO oxidation, the active oxygen sites play a more vital role than the acid sites.

Boosting propane combustion over Pt/WO3 catalyst by activating interface oxygen species

Surface active oxygen species in heterogeneous catalyst material is very vital for driving catalytic volatile organic compounds (VOCs) oxidation, but it still remains challenging to effectively modulate such active oxygen species. Herein, the interfacial oxygen species in Pt/WO3 catalyst is conveniently activated by a heating treatment under nitrogen flow. The obtain Pt/WO3-N2-T (T = 200, 400, 600, represents the calcination temperature) shows much superior catalytic activity than the bare Pt/WO3 catalyst, particularly for the Pt/WO3-N2-400 catalyst with T95 of only 250 °C (T95 of Pt/WO3 = 350 °C). The changes of catalyst structure during heating treatment in nitrogen flow contributes to the improved activity, including re-dispersed WO3 support and Pt nanoparticles. More importantly, the surface oxygen species in the Pt/WO3-N2-400 catalyst is more active than that of the bare Pt/WO3 catalyst, which is generated by removing hydroxyl groups and its residual oxygen species activated by nearby Pt species. These novel findings provide the strategy to rationally activate surface oxygen in the heterogeneous catalyst materials for catalytic oxidation reaction.

Promotion of Rh-based La2Zr2O7 type catalysts with the transition metals to improve sulfur-tolerance in diesel reforming

Several Rh-based La2Zr2O7 type catalysts promoted by the transition metals (Mn, Fe, and Co respectively) were synthesized and used to reform n-hexadecane (a diesel surrogate) that contains 50 ppm dibenzothiophene for hydrogen production. Compared to Co-LaZrRh and Mn-LaZrRh, the Fe-LaZrRh catalyst exhibited the best hydrogen extraction capability and sulfur tolerance. This is probably due to the introduction of Fe, which not only enhances the Rh dispersion, but also facilitates the formation of electron-deficient Rh sites and the generation of oxygen vacancies. Additionally, electron-deficient Rh sites can hinder the formation of an irreversible sulfur-metal bond, thus resulting in better sulfur tolerance and thermal stability. Finally, the generated oxygen vacancies may also activate steam to form surface active oxygen species, which help remove the deposited carbon on the catalyst surface. In summary, the developed Fe-LaZrRh catalyst performed the best in the steam reforming of n-hexadecane containing 50 ppm sulfur, which deserves further exploration for future applications.