Silica‐Encapsulated Pt‐Sn Intermetallic Nanoparticles: A Robust Catalytic Platform for Parahydrogen‐Induced Polarization of Gases and Liquids

Abstract

Recently, a facile method for the synthesis of size-monodisperse Pt, Pt Sn, and PtSn intermetallic nanoparticles (iNPs) that are confined within a thermally robust mesoporous silica (mSiO ) shell was introduced. These nanomaterials offer improved selectivity, activity, and stability for large-scale catalytic applications. Here we present the first study of parahydrogen-induced polarization NMR on these Pt-Sn catalysts. A 3000-fold increase in the pairwise selectivity, relative to the monometallic Pt, was observed using the PtSn@mSiO catalyst. The results are explained by the elimination of the three-fold Pt sites on the Pt(111) surface. Furthermore, Pt-Sn iNPs are shown to be a robust catalytic platform for parahydrogen-induced polarization for in vivo magnetic resonance imaging.

Selective Single‐Site Pd−In Hydrogenation Catalyst for Production of Enhanced Magnetic Resonance Signals using Parahydrogen

“…The scope of heterogeneous catalysts which are suitable for PHIP increased significantly in the past 10 years. For instance, PHIP was successfully observed over various metal catalysts such as Rh, Pt, Pd, Ir, Au, Cu, bimetallic systems Pt−Sn, Pd−Au, Pd−M (M=Sn, Zn, Ag, Mn, Pb, Au) supported on support materials such as SiO 2 , ZrO 2 , Al 2 O 3 , TiO 2 , Al−Si fiberglass, chitosan, carbon nanotubes . Moreover, the PHIP effect was demonstrated for bulk Pt metal and several metal oxides (PtO 2 , PdO and CeO 2 ).…”

“…These single‐site centers behave similarly to the metal centers of homogeneous catalysts in catalytic reactions and thus, can be expected to accomplish pairwise addition of H 2 to a substrate. So far the largest contribution of pairwise hydrogen addition (10.9 %) was observed with the use of silica‐encapsulated Pt‐Sn intermetallic nanoparticles in propene hydrogenation, but the overall conversion estimated as 0.5 % is too low for MRI applications. Here, a Pd‐based catalyst with the single‐site character of the distribution of active sites was utilized for the production of propene with significant levels of both hyperpolarization and conversion (9.3 % (1.7 % observable, without corrections) and 20 %, respectively) during selective heterogeneous hydrogenation of propyne and for subsequent MR visualization of this hyperpolarized propene.…”

Parahydrogen‐Based Hyperpolarization for Biomedicine

“…HET-PHIP effects were also successfully observed using heterogeneous catalysts comprising Pt and Pd nanoparticles supported on γ-Al 2 O 3 , [79] and later for many other supported metals (e.g., Rh, Ir, Co, Ni, Au, Cu) catalysts in gas, liquid and aqueous phase hydrogenations. [11–12, 25, 27, 78f, 78g, 80] Variation of the type of metal, metal particle size [80a, 80d, 81] and shape, [80e, 80h] type of support [80a, 80d, 80g, 80i] and reaction conditions were all shown to influence the magnitude of the PHIP effect. Polarization transfer from 1 H to heteronuclei ( 13 C, 15 N) during heterogeneous hydrogenation [9b, 62a, 62b] helps to increase the hyperpolarization lifetime significantly, and is particularly important for potential biomedical applications along with the use of aqueous media.…”

“…[27] (A) Reaction scheme and 1 H-NMR spectra of acetate which was formed in methanol-d 4 by pairwise addition of pH 2 at high field using Pt, Pt 3 Sn, or PtSn intermetallic nanoparticle catalysts with different pairwise selectivity. The typical antiphase multiplets were observed (a, b).…”

Single‐Site Heterogeneous Catalysts: From Synthesis to NMR Signal Enhancement

“…An approach described in recent work by Bowers et al. aimed to increase the pairwise selectivity of heterogeneous PHIP catalysts . The highest pairwise selectivity of 10.9 % was observed with silica‐encapsulated Pt−Sn intermetallic nanoparticles in propene hydrogenation, but the overall conversion was estimated to be 0.5 %.…”