Low-temperature carbon monoxide oxidation catalysed by regenerable atomically dispersed palladium on alumina

Abstract

Catalysis by single isolated atoms of precious metals has attracted much recent interest, as it promises the ultimate in atom efficiency. Most previous reports are on reducible oxide supports. Here we show that isolated palladium atoms can be catalytically active on industrially relevant g-alumina supports. The addition of lanthanum oxide to the alumina, long known for its ability to improve alumina stability, is found to also help in the stabilization of isolated palladium atoms. Aberration-corrected scanning transmission electron microscopy and operando X-ray absorption spectroscopy confirm the presence of intermingled palladium and lanthanum on the g-alumina surface. Carbon monoxide oxidation reactivity measurements show onset of catalytic activity at 40°C. The catalyst activity can be regenerated by oxidation at 700°C in air. The high-temperature stability and regenerability of these ionic palladium species make this catalyst system of potential interest for low-temperature exhaust treatment catalysts.

Regenerable Subnanometer Pd Clusters on Zirconia for Highly Selective Hydrogenation of Biomass-Derived Succinic Acid in Water

“…Aberration-corrected high-angle annual dark-filed scanning transmission electron microscopy (AC-HAADF-STEM) can recognize the atomically dispersed noble metal on the support, providing direct information about the surface structure of the catalysts [9,31,32]. Here, it was employed to characterize the dispersion and identification of the Pd clusters in the materials.…”

“…The overlapped atom intensities are fitted using two-dimensional (2D) Gaussian functions by facile background subtraction so that the subnanometer Pd cluster can be recognized clearly in the AC-HAADF-STEM images (Figure 1c-e) [9]. It is known that the contrast of atoms in AC-HAADF-STEM is generated from the nucleus by electron scattering.…”

“…However, the stability and recyclability remain a challenge because the isolated clusters or single atoms are mobile and readily sintered under high reaction temperatures [7]. To the best of our knowledge, there are only a few contributions regarding the atomically dispersed Pd catalysts that are active and stable at high temperatures [8,9], while those of Au and Pt catalysts have been widely reported [10][11][12][13]. Atomically dispersed Pd on graphene shows excellent durability against deactivation during 100 h of reaction time [8].…”

“…Atomically dispersed Pd on graphene shows excellent durability against deactivation during 100 h of reaction time [8]. Peterson et al [9] prepared Pd species on La-doped γ-alumina supports that can be easily regenerated at 973 K through oxidation using air. Moreover, the addition of atomically dispersed La 3+ ions into the alumina support plays a key role in helping to stabilize and disperse isolated Pd atoms on the alumina surface.…”

Time Resolved Operando X-ray Techniques in Catalysis, a Case Study: CO Oxidation by O2 over Pt Surfaces and Alumina Supported Pt Catalysts

“…As such, for Pt supported upon simple oxides the LH mechanism fundamentally limits their application to CO oxidation at, for example, ambient temperature; a fact that might be regarded as a major driver for the intense research that has been undertaken in recent years to achieve this goal using other metals (most notably Au [17][18][19][20][21]) and more complex, and reducible support systems [17][18][19][20][21][22][23][24][25][26][27][28][29]. These approaches aim to favorably modify the fundamental molecular interactions required for this conversion by weakening the M-CO interaction whilst still providing a kinetically appropriate supply of dissociated oxygen through an LH scenario and/or, in the case of employment of reducible oxides, introducing of another possible source of oxygen, and moving the whole reaction paradigm toward the MvK.…”