Silica-Confined Pt₃Sn Clusters for Propane Dehydrogenation

Abstract

Silica-confined Pt x Sn1–x (x = 0.6–1.0) clusters were examined for the dehydrogenation of propane to propylene, in terms of the activity and selectivity. It was found that the Pt0.8Sn0.2 cluster of 1.5 nm, encapsulated in a porous silica particle of about 20 nm, was highly active and selective, yielding propane conversion of 20% and propylene selectivity of 97% at 873 K. The specific activity, based on Pt mass, was approximately two times greater than that over the Pt cluster at a similar size. The Pt3Sn alloy in a face-centered cubic structure served as the active phase, in which Pt and Sn atoms catalyzed synergistically. The Pt atoms dominated the activity, while the Sn atoms controlled the selectivity by blocking the low-coordinated Pt sites for cracking the C–C bond. Structural analysis on the spent catalysts revealed that both the size and the atomic arrangement of the metal clusters remained unchanged, evidencing that the spatial confinement of porous silica physically restricted the aggregation and sintering of the smaller metal clusters at such a high temperature and under the highly reductive gases. Instead, accumulated cokes were mainly responsible for the deactivation.

SnOx-Decorated Pt Catalysts for the Reductive N-Methylation of Quinoline with Methanol

“…Temperature programmed reduction in hydrogen atmosphere (H 2 -TPR) and diffuse reflectance infrared Fourier transform of CO adsorption (CO-DRIFT) were further employed to illustrate the SnO x effects on the Pt-SnO x /Al 2 O 3 catalysts. The H 2 -TPR results of Pt/Al 2 O 3 and SnO x /Al 2 O 3 unveiled reduction peaks at approximately 242 and 429 °C (Figure c), corresponding to the reduction of PtO x and SnO x . , Contrarily, for three Pt-SnO x /Al 2 O 3 catalysts, the reduction peaks of PtO x occurred at a higher temperature (268 °C), while the reduction peak of SnO x appeared at a lower temperature (420 °C). This observation is attributed to the hydrogen spillover effect of Pt and the strong interaction between PtO x and SnO x species, respectively.…”

“…However, when the n Sn /n Pt ratio was further increased to 3.0, the percentage of both Sn 0 and Sn 2+ decreased due to more SnO x strongly interacted with SnO x . 48,49 Contrarily, for three Pt-SnO x /Al 2 O 3 catalysts, the reduction peaks of PtO x occurred at a higher temperature (268 °C), while the reduction peak of SnO x appeared at a lower temperature (420 °C). This observation is attributed to the hydrogen spillover effect of Pt and the strong interaction between PtO x and SnO x species, respectively.…”

“…CO–DRIFT spectra for Pt-SnO x /Al 2 O 3 catalysts exhibited similar CO adsorption patterns to Pt/Al 2 O 3 in the range of 1830 to 2100 cm –1 (Figure d). These bands are commonly assigned to the bridged-adsorbed CO on two contiguous metallic Pt 0 atoms (1838–1885 cm –1 ), linear-bonded CO on metallic nanoparticle surfaces at either well-coordinated (2086 cm –1 ) or under-coordinated (2068 cm –1 ) Pt 0 sites, and linear-bonded CO on oxidized Pt δ+ (2124 cm –1 ). − , These results indicate that all Pt-SnO x /Al 2 O 3 catalysts still exhibit the metallic Pt 0 ensembles but do not form the identifiable PtSn alloy. Notably, the intensity of adsorbed CO bands on well-coordinated Pt 0 sites become higher, while that on under-coordinated (2030–2070 cm –1 ) Pt 0 sites become lower.…”

“…Pt-Based materials exhibit outstanding catalytic activity for (transfer) hydrogenation, , C–N coupling reactions, and methanol-involved transformations. ,, However, there remains additional potential to enhance the catalytic capability of Pt catalysts for methanol-involved reactions, ,, particularly under mild (≤130 °C) and environmentally benign reaction conditions (without base additives). It is established that modifying the active metal with a second component (e.g., SnO x , − In 2 O 3 , and MoO x ) is a reliable method to enhance the catalytic efficiency of Pt-based catalysts, surpassing individual Pt catalysts in various C–H bonds activation processes (such as alkane dehydrogenation − and methanol reforming). To achieve an efficient catalyst, a series of second component-decorated Pt materials with diverse metal oxide promoters (Table , entries 1–5) and supports (Table , entries 6–10), and their catalytic performances for the direct N -methylation of quinoline ( 1a ) with methanol were also investigated.…”

Influence of Thermal Cracking on Propylene Selectivity in Catalytic Propane Dehydrogenation Using SnOx–SiO2 Catalyst

“…Catalytic propane dehydrogenation (PDH) is a well-known reaction to produce propylene, which can be used as a precursor for a wide variety of plastic products and other value-added chemicals and has been studied for many years. Many catalysts can activate this reaction, for example, metal-based catalysts like Pt, Pd, and Ni; metal oxide-based catalysts like CrO x , VO x , GaO x , SnO x , ZrO 2 , and MoO x ; and other formulations like metal sulfides, carbides, nitrides, and carbon-based materials. − However, these catalysts have their weaknesses, for example, elevated costs in the case of noble metals, high toxicity in the case of Cr, fast coking-related deactivation in strong acid catalysts, irreversible deactivation because of the loss of sulfur in metal sulfide catalysts, and undesired hydrogenolysis as a side reaction in the metal catalysts. − Hence, many research interests are focused on developing and exploring new catalysts with high efficiency, low cost, and environmental friendliness. One of them is a silica-supported tin oxide catalyst, which shows impressive stability as a distinctive point.…”