Model catalyst studies of active sites and metal support interactions on vanadia and vanadia-supported catalysts

Abstract The influence of Al2O3–ZrO2 and TiO2–ZrO2 supports on NiMo-supported catalysts at a different sulfur concentration in a model hydrodeoxygenation (HDO)-hydrodesulfurization (HDS) co-processing reaction has been studied in this work. A competition effect between phenol and dibenzothiophene (DBT) for active sites was evidenced. The competence for the active sites between phenol and DBT was measured by comparison of the initial reaction rate and selectivity at two sulfur concentrations (200 and 500 ppm S). NiMo/TiO2–ZrO2 was almost four-fold more active in phenol HDO co-processed with DBT than NiMo/Al2O3–ZrO2 catalyst. Consequently, more labile active sites are present on NiMo/TiO2–ZrO2 than in NiMo/Al2O3–ZrO2 confirmed by the decrease in co-processing competition for the active sites between phenol and DBT. DBT molecules react at hydrogenolysis sites (edge and rim) preferentially so that phenol reacts at hydrogenation sites (edge and edge). However, the hydrogenated capacity would be lost when the sulfur content was increased. In general, both catalysts showed similar functionalities but different degrees of competition according to the highly active NiMoS phase availability. TiO2–ZrO2 as the support provided weaker metal-support interaction than Al2O3–ZrO2, generating a larger fraction of easily reducible octahedrally coordinated Mo- and Ni-oxide species, causing that NiMo/TiO2–ZrO2 generated precursors of MoS2 crystallites with a longer length and stacking but with a higher degree of Ni-promotion than NiMo/Al2O3–ZrO2 catalyst.

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Pd Supported Catalysts with Intrinsic Surface Electropositive Sites for Improved Selective Hydrogenation of Cinnamaldehyde

10.26434/chemrxiv.12964598.v1 ◽

2020 ◽

Author(s):

Surya Kumar Vatti ◽

Kandasamy Konda R Krishnamurthy ◽

Balasubramanian Viswanathan

Keyword(s):

Catalyst Surface ◽

Supported Catalysts ◽

Chemical Reduction ◽

Colloidal Suspension ◽

Surface Concentration ◽

Pd Nanoparticles ◽

Reduction Peak ◽

Metal Support ◽

Metal Support Interactions ◽

Mild Temperature

Uniform-spherical Pd nanoparticles (NPs) supported catalysts were prepared by a mild-temperature chemical reduction method. Pd colloidal suspension was wet-impregnated on various supports, P25-TiO2, SiO2, and γ-Al2O3. In XPS, asymmetric Pd 3d5/2 peak reveals % surface concentration of Pd2+ and Pd0 species. The surface Pd2+/Pd0 ratio on the catalyst surface varied between ~1 to 0.15 depending on strong-metal support interactions (SMSI) inferred from XPS and H2-TPR studies. A linear correlation between Pd2+/Pd0 ratio and turnover frequency (TOF) was observed, with 1% Pd/P25-TiO2 showing the highest TOF/selectivity with Pd2+/Pd0 ratio ~1.0, whereas 1% Pd/γ-Al2O3 showed the lowest TOF/selectivity with lowest Pd2+/Pd0 ratio 0.15. Interestingly, H2-TPR reveals PdH decomposition peaks along with the Ti4+ reduction peak, and XPS Ti 2p of 1% Pd/P25-TiO2 indicates the presence of Ti3+ in TiO2 lattice, which may have generated due to H2-spillover from Pd to P25-TiO2. Hence, we observed excellent COL selectivity (~90%) and 100 % conversion with 1.5% Pd/P25-TiO2 catalyst. Excellent COL selectivity may be ascribed to small Pd NPs (~3 nm) with intrinsic surface electropositive sites (Pd2+) created by partial reduction on the catalyst surface along with SMSI. These electropositive sites (Pd2+) promote preferential C=O adsorption. On the other hand, post-reduced catalyst in H2 @300 °C (1% Pd/P25-TiO2-PRH2) with large Pd NPs (~7 nm) showed significant selectivity loss (>50 %), which confirm significance of small Pd NPs with electropositive sites.

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Inside Cover: Novel, Highly Conductive Pt/TiO2Thin-Film Model Catalyst Electrodes: The Role of Metal-Support Interactions (ChemElectroChem 10/2016)

ChemElectroChem ◽

10.1002/celc.201600568 ◽

2016 ◽

Vol 3 (10) ◽

pp. 1516-1516

Author(s):

Christian Gebauer ◽

Doris Hoffmann ◽

Zenonas Jusys ◽

R. Jürgen Behm

Keyword(s):

Model Catalyst ◽

Film Model ◽

Metal Support ◽

Metal Support Interactions

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Reaction Pathway for Coke-Free Methane Steam Reforming on a Ni/CeO2 Catalyst: Active Sites and the Role of Metal–Support Interactions

ACS Catalysis ◽

10.1021/acscatal.1c01604 ◽

2021 ◽

pp. 8327-8337

Author(s):

Agustín Salcedo ◽

Pablo G. Lustemberg ◽

Ning Rui ◽

Robert M. Palomino ◽

Zongyuan Liu ◽

...

Keyword(s):

Steam Reforming ◽

Active Sites ◽

Reaction Pathway ◽

Methane Steam Reforming ◽

Methane Steam ◽

Metal Support ◽

Metal Support Interactions

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Pd Supported Catalysts with Intrinsic Surface Electropositive Sites for Improved Selective Hydrogenation of Cinnamaldehyde

10.26434/chemrxiv.12964598 ◽

2020 ◽

Author(s):

Surya Kumar Vatti ◽

Kandasamy Konda R Krishnamurthy ◽

Balasubramanian Viswanathan

Keyword(s):

Catalyst Surface ◽

Supported Catalysts ◽

Chemical Reduction ◽

Colloidal Suspension ◽

Surface Concentration ◽

Pd Nanoparticles ◽

Reduction Peak ◽

Metal Support ◽

Metal Support Interactions ◽

Mild Temperature

Uniform-spherical Pd nanoparticles (NPs) supported catalysts were prepared by a mild-temperature chemical reduction method. Pd colloidal suspension was wet-impregnated on various supports, P25-TiO2, SiO2, and γ-Al2O3. In XPS, asymmetric Pd 3d5/2 peak reveals % surface concentration of Pd2+ and Pd0 species. The surface Pd2+/Pd0 ratio on the catalyst surface varied between ~1 to 0.15 depending on strong-metal support interactions (SMSI) inferred from XPS and H2-TPR studies. A linear correlation between Pd2+/Pd0 ratio and turnover frequency (TOF) was observed, with 1% Pd/P25-TiO2 showing the highest TOF/selectivity with Pd2+/Pd0 ratio ~1.0, whereas 1% Pd/γ-Al2O3 showed the lowest TOF/selectivity with lowest Pd2+/Pd0 ratio 0.15. Interestingly, H2-TPR reveals PdH decomposition peaks along with the Ti4+ reduction peak, and XPS Ti 2p of 1% Pd/P25-TiO2 indicates the presence of Ti3+ in TiO2 lattice, which may have generated due to H2-spillover from Pd to P25-TiO2. Hence, we observed excellent COL selectivity (~90%) and 100 % conversion with 1.5% Pd/P25-TiO2 catalyst. Excellent COL selectivity may be ascribed to small Pd NPs (~3 nm) with intrinsic surface electropositive sites (Pd2+) created by partial reduction on the catalyst surface along with SMSI. These electropositive sites (Pd2+) promote preferential C=O adsorption. On the other hand, post-reduced catalyst in H2 @300 °C (1% Pd/P25-TiO2-PRH2) with large Pd NPs (~7 nm) showed significant selectivity loss (>50 %), which confirm significance of small Pd NPs with electropositive sites.

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