Charge transfer between metal sites and supports is crucial for catalysis. Redox‐inert supports are usually unfavorable due to their less electronic interaction with metal sites, which, we ...demonstrate, is not always correct. Herein, three metal–organic frameworks (MOFs) are chosen to mimic inert or active supports for Pt nanoparticles (NPs) and the photocatalysis is studied. Results demonstrate the formation of a Schottky junction between Pt and the MOFs, leading to the electron‐donation effect of the MOFs. Under light irradiation, both the MOF electron‐donation effect and Pt interband excitation dominate the Pt electron density. Compared with the “active” UiO‐66 and MIL‐125 supports, Pt NPs on the “inert” ZIF‐8 exhibit higher electron density due to the higher Schottky barrier, resulting in superior photocatalytic activity. This work optimizes metal catalysts with non‐reducible supports, and promotes the understanding of the relationship between the metal–support interaction and photocatalysis.
Platinum nanoparticles are supported on different MOFs, including non‐reducible ZIF‐8 and reducible UiO‐66 and MIL‐125. Unexpectedly, the Pt/ZIF‐8 exhibits higher activity than Pt/UiO‐66 and Pt/MIL‐125 in the photocatalytic benzylamine oxidative coupling reaction. The different electron transfer behaviors among these photocatalysts lead to the highest Pt electron density on ZIF‐8 toward O2 activation, accounting for its superior activity.
Full text
Available for:
BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SBCE, SBMB, UL, UM, UPUK
Display omitted
•Pt(acac)2 precursor ensured even PtNP dispersion on α-MnO2 nanorods.•Surprisingly, increasing the Pt loading induced a transition from α-MnO2 to Mn5O8.•XPS showed a decrease in ...Pt(IV) and Pt(II) with Pt loading, while Pt(0) increased.•Pt/MnO2 nanorods displayed excellent catalytic activity for 4-NP to 4-AP reduction.•The presence of Pt(IV) is not a limiting factor for the catalytic conversion of 4-NP to 4-AP.
α-MnO2 nanorods (NRs) were synthesized by microwave irradiation and used as supports for platinum nanoparticles by wet impregnation with Pt(acac)2 as precursor. XRD analysis revealed that the samples without platinum (sample MP0) and with 1 % platinum (sample MP1) contained tetragonal α-MnO2. Samples with 3 % (sample MP3) and 5 % (sample MP5) of platinum contained monoclinic Mn5O8 in addition to α-MnO2, with Mn5O8 dominating in sample MP5. Rietveld analysis showed that the lattice parameters of α-MnO2 increased slightly with Pt loading. SEM and STEM showed that higher Pt loadings resulted in shorter nanorods and different sizes and dispersions of PtNPs on their surface. XPS results showed a decrease in Pt(IV) and Pt(II) concentration with Pt loading, while Pt(0) increased. NEXAFS results showed the presence of Mn(II) in MP3 and MP5, which is consistent with XRD results detecting Mn5O8. The catalytic activity of the Pt/α-MnO2 nanorods was tested in the catalytic reduction of 4-nitrophenol to 4-aminophenol. MP1, with the lowest platinum content, exhibited the highest mass normalized rate constant kapp/mPt of 1.8 × 104 s−1 g−1. The study suggests that the presence of Pt(IV) is not a limiting factor for the catalytic reduction of 4-NP to 4-AP.
Full text
Available for:
GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Display omitted
•Pd catalysts on different iron oxide supports were synthesized by co-precipitation.•Characterization by bulk- and surface-sensitive method reveals reducibility of the support.•Strong ...metal–support interaction is described by Pd particles that are overgrown by FeOx.•The strong metal–support interaction state is highly active in CO oxidation, but not stable.
Pd/FeOx catalysts were prepared by co-precipitation and characterized before and after reduction using X-ray powder diffraction, thermal analysis, CO chemisorption, electron microscopy, and X-ray photoelectron spectroscopy. Results give evidence for the encapsulation of palladium particles by iron oxide after reduction at high temperatures (523K). Oxidation of carbon monoxide was applied as test reaction to characterize catalyst samples in different states. Strong metal–support interactions significantly enhance catalytic activity for oxidation of carbon monoxide. However, this state is not stable under the applied reaction conditions. Catalyst deactivation occurs in two ways: (1) via changes in the oxidation state of iron species and (2) due to sintering of palladium particles.
Full text
Available for:
GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
Display omitted
•Exclusive hydrogenation to benzyl alcohol and aniline over supported Au.•TOF increased with decreasing Au size (8- 4 nm); lower TOF over Au <3nm.•CHO and NO2 repulsion by Auδ+ and ...strong binding to oxygen vacancies lower TOF.•Auδ− on non-reducible Al2O3 favours selective formation of benzyl alcohol.•Higher temperatures (>413K) promote hydrogenolysis to toluene and benzene.
A range of oxides (γ-Al2O3, TiO2, ZrO2, CeO2, α-Fe2O3 and Fe3O4) with different redox properties were used to support nano-scale (mean=2–8nm) Au and employed in the gas phase hydrogenation of benzaldehyde and nitrobenzene. The catalysts were subjected to TPR, H2/O2 titration, H2 TPD, XRD, TEM/STEM and XPS analysis. The supported Au phase promoted partial reduction of the reducible supports through the action of spillover hydrogen (based on TPD), which generated surface oxygen vacancies (demonstrated by O2 titration) that inhibit Au particle sintering during catalyst activation. Electron transfer to generate charged Au species (determined by XPS) correlates with support ionisation potential. Higher nitrobenzene hydrogenation (to aniline) TOFs were recorded relative to benzaldehyde where rate increased with decreasing Au size (from 8 to 4nm) with measurably lower TOF over Au <3nm. Strong binding of CHO and NO2 functions to oxygen vacancies resulted in lower hydrogenation rates. Higher temperatures (>413K) promoted benzaldehyde hydrogenolysis to toluene and benzene. The formation of Auδ− on non-reducible Al2O3 favoured selective reduction of CHO with full selectivity to benzyl alcohol at 413K.
Full text
Available for:
GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
Charge transfer between metal sites and supports is crucial for catalysis. Redox‐inert supports are usually unfavorable due to their less electronic interaction with metal sites, which, we ...demonstrate, is not always correct. Herein, three metal–organic frameworks (MOFs) are chosen to mimic inert or active supports for Pt nanoparticles (NPs) and the photocatalysis is studied. Results demonstrate the formation of a Schottky junction between Pt and the MOFs, leading to the electron‐donation effect of the MOFs. Under light irradiation, both the MOF electron‐donation effect and Pt interband excitation dominate the Pt electron density. Compared with the “active” UiO‐66 and MIL‐125 supports, Pt NPs on the “inert” ZIF‐8 exhibit higher electron density due to the higher Schottky barrier, resulting in superior photocatalytic activity. This work optimizes metal catalysts with non‐reducible supports, and promotes the understanding of the relationship between the metal–support interaction and photocatalysis.
Platinum nanoparticles are supported on different MOFs, including non‐reducible ZIF‐8 and reducible UiO‐66 and MIL‐125. Unexpectedly, the Pt/ZIF‐8 exhibits higher activity than Pt/UiO‐66 and Pt/MIL‐125 in the photocatalytic benzylamine oxidative coupling reaction. The different electron transfer behaviors among these photocatalysts lead to the highest Pt electron density on ZIF‐8 toward O2 activation, accounting for its superior activity.
Full text
Available for:
BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SBCE, SBMB, UL, UM, UPUK
This publication describes the application of the direct anionic exchange method (DAE) in the preparation of gold nanoparticles supported of different oxide materials. Some of the most frequently ...used metal oxides in the gold catalysis are investigated, i.e., TiO
2, ZrO
2, CeO
2 and Al
2O
3, as well as some less typical such as SiO
2 and MgO. The formation of gold nanoparticles has been proven by transmission electron microscopy with particles size ranging between 1.9 and 3
nm for all catalysts.
▪
This publication describes the application of the direct anionic exchange method (DAE) in the preparation of gold nanoparticles supported upon different oxide materials. Some of the metal oxides most frequently used in gold catalysis are investigated, i.e., TiO
2, ZrO
2, CeO
2 and Al
2O
3, as well as some of those less typical such as SiO
2 and MgO. All of these supports have been studied comparatively for their acid–base and redox properties. It was found that the method of preparation is successful on a quantitative level for all of the supports, having an isoelectric point between 4 and 7. The formation of gold nanoparticles was confirmed by transmission electron microscopy with particle size ranging between 1.9 and 3
nm for each catalyst. All gold catalysts were tested in the CO oxidation reaction and it was concluded that gold catalysts supported on reducible type metal oxides such as CeO
2, TiO
2 and ZrO
2 are generally more active.
Full text
Available for:
GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
Display omitted
Regulating the selectivity between CO and CH4 during CO2 hydrogenation is a challenging research topic. Previous research has indicated that potassium (K) modification can adjust the ...product selectivity by regulating the adsorption strength of formate/CO* intermediates. Going beyond the regulation mechanism described above, this study proposes a K-guided selectivity control method based on the regulation of key intermediates HCO*/H3CO* for Ni catalysts supported on reducible carrier CeO2. By incorporating K, the CO selectivity of CO2 hydrogenation shifts from around 25.4% for Ni/CeO2 to approximately 93.8% for Ni/CeO2-K. This can be attributed to K modification causes electron aggregation in the bonding regions of HCO* and H3CO* intermediates, thus enhancing their adsorption strength. Consequently, the reaction pathway from HCO*/H3CO* to CH4 is limited, favoring the decomposition of formates to CO products. Moreover, the addition of K leads to a moderate decrease in CO2 conversion from 55.2% to 48.6%, which still surpasses values reported in most other studies. This reduction is associated with a decline in reducible Ni species and oxygen vacancy concentration in Ni/CeO2-K. As a result, the adsorption capacity for CO2 and H2 reduces, ultimately reducing CO2 hydrogenation activity.
Full text
Available for:
GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
The particle size of CeO2 was controlled to study the selectivity toward CO production in CO2 hydrogenation over Co/CeO2 catalysts using ambient-pressure conditions. CeO2 was selected as a typical ...catalyst support, and it was pretreated by calcination at 450, 750, 900, and 1000 °C, which increases the CeO2 particle size prior to impregnation to prepare a series of 5 wt % Co/CeO2. As a result of catalytic testing, it was found that the CO selectivity can be promoted from 24 ± 2% to 49 ± 1% when the CeO2 is calcined at 1000 °C. We propose that the CeO2 calcination at high temperatures improved its reducibility, strengthened CO adsorption, and weakened H adsorption over the surface of the impregnated Co nanoparticles. Our proposed explanation toward the increased CO selectivity was supported using in situ techniques, i.e., in situ CO DRIFTS and in situ XPS and TEM characterization. This work provides distinctive insight into the relationship between metal–support interaction and the controlled product selectivity in CO2 hydrogenation.
Full text
Available for:
IJS, KILJ, NUK, PNG, UL, UM
Support effects play a pivotal role in most heterogeneous catalysts, and understanding the underlying catalytic mechanism is crucial for guiding catalyst design and optimizing performance. In this ...study, we conduct a kinetics and mechanistic investigation into the support effects of Cu catalysts in hydrogen combustion by comparing reducible and nonreducible supports. Multiple characterization techniques are employed to comprehend the support effects, with the reducible support and low-valence Cu species highlighted for the most active Cu/ZrO2 catalyst. A redox-based kinetics strategy is further proposed by decoupling the reduction step and oxidation step. The as-obtained reduction and oxidation rate diagram indicates a significantly enhanced reduction rate for the reducible supported catalyst, attributed to the abundant surface oxygen vacancy for the generation of hydroxyl intermediates. These efforts aim to develop more efficient kinetics-based techniques for unraveling the nature of support effects, thereby offering a rational approach to designing highly active catalysts.
Display omitted
•A redox-based strategy is developed to decipher the support effects of Cu catalysts•The reducible support and low-valence Cu species promote catalytic hydrogen combustion•A reduction and oxidation rate diagram is established to guide catalyst design
Understanding the catalytic mechanism of support effects is crucial for tunable catalysis. Here, Zhang et al. propose a redox-based kinetics strategy by decoupling the reduction step and oxidation step to highlight the important roles of low-valence Cu species and oxygen vacancies in Cu catalysts for catalytic hydrogen combustion.
Full text
Available for:
GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Pyrolysis and liquefaction biocrudes obtained from lignocellulose are rich in phenolic compounds that can be converted to renewable aromatics. In this study, Pt catalysts on reducible metal oxide ...supports (Nb2O5, TiO2), along with irreducible ZrO2 as a reference, were investigated in the liquid‐phase hydrodeoxygenation (HDO) of 4‐propylphenol (350 °C, 20 bar H2, organic solvent). The most active catalyst was Pt/Nb2O5, which led to the molar propylbenzene selectivity of 77 %, and a yield of 75 % (98 % conversion). Reducible metal oxide supports provided an increased activity and selectivity to the aromatic product compared to ZrO2, and the obtained results are among the best reported in liquid‐phase. The reusability of the spent catalysts was also studied. The spent Pt/Nb2O5 catalyst provided the lowest conversion, while the product distribution of the spent Pt/ZrO2 catalyst changed towards oxygenates. The results highlight the potential of pyrolysis or liquefaction biocrudes as a source of aromatic chemicals.
Surface selection: Hydrodeoxygenation of 4‐propylphenol to propylbenzene was studied with Pt catalysts on reducible metal oxide supports in liquid‐phase reaction with organic solvent. High propylbenzene selectivities were obtained, and catalyst activity decreased in order: Pt/Nb2O5>Pt/TiO2>Pt/ZrO2.
Full text
Available for:
FZAB, GIS, IJS, IZUM, KILJ, NLZOH, NUK, OILJ, PILJ, PNG, SAZU, SBCE, SBMB, UL, UM, UPUK
PDF
