Atomically Dispersed Pd Supported on Zinc Oxide for Selective Nonoxidative Ethanol Dehydrogenation

Abstract

Atomically dispersed Pd/ZnO was synthesized using a facile method. We found that 0.07 wt % Pd was isolated and positively charged on ZnO synthesized using a solvothermal method. By contrast, Pd clusters were formed on commercial ZnO, with the difference between the two supports residing in their different number of defects and surface area. Pd atoms are selective in the ethanol dehydrogenation reaction to form acetaldehyde and H2 exclusively, while Pd clusters decompose ethanol to form CO and CH4 as byproducts. Our work proves that the structure of Pd affects the selectivity of the reaction, and isolated Pd sites, unlike the contiguous Pd metal sites, catalyze the selective C–H bond scission while keeping the C–C bond intact. Pd atoms also showed higher stability in the reaction, since they did not suffer from coke formation. This work provides new insights to enable the design of selective and stable Pd-based catalysts for alcohol conversion reactions.

Zinc oxide-modified mordenite as an effective catalyst for the dehydrogenation of (bio)ethanol to acetaldehyde

“…The major products produced from ethanol conversion over NiO/Na-MOR- (7) and PdO/Na-MOR-(7) were CH 4 and CO suggesting that acetaldehyde was formed initially but subsequently underwent rapid decarbonylation by the catalysts, a reaction observed for several homogenous Ni and Pd catalysts, 43,44 alongside supported Pd clusters. 27 At TOS <0.5 h an induction period in acetaldehyde productivity is observed for some of the catalysts (ZnO/Na-MOR-(7), Co 3 O 4 /Na-MOR- (7) and Fe 2 O 3 /Na-MOR-(7)), during which period ethylene is the major product (Table S2 and Fig. S3 †).…”

“…pXRD samples were sieved to <177 mm (80 mesh), mounted onto either glass or silicon (9 1 1) slide holders by adhesion with petroleum jelly and rotated during data acquisition. Solid-state 27 Al NMR spectra were acquired on a Varian VNMRS spectrometer operating at 104.198 MHz with a spinning rate of approx. 14 kHz.…”

“…Fig. 5B shows the solid-state 27 Al NMR spectra of each ZnO/Na-MOR-(7) material and conrms that aluminium exists solely in tetrahedral framework positions (d Al z 60 ppm) therefore ruling out any effect of extra-framework alumina on catalysis. 46 Further, SEM imaging of the four catalyst variations did not show evidence of any change in catalyst morphology or large ZnO clusters on the surface of the catalyst crystals (Fig.…”

“…[50][51][52][53][54] Fig. 7 shows the pXRD patterns (A) and 27 Al solid-state NMR spectra (B) for ZnO/M-MOR-(7) materials (where M ¼ Na, K, Rb, or Cs) indicating successful retention of both an MFI structure and tetrahedral aluminium sites following catalyst preparation, however, the low angle reections (2q < 15 ) within Fig. 7A are decreased in intensity for ZnO/Rb-MOR- (7) and ZnO/Cs-MOR- (7).…”

“…10 Many current systems for direct dehydrogenation of ethanol typically focus around the use of supported metal nanoparticles and metal oxides, with related emerging technologies seeking to prevent sintering and deactivation of such supported systems. [27][28][29][30][31] In particular, zeolite and porous silica materials have become an area of considerable interest as favourable supports for metal species owing to their ability to stabilize metal ions and direct metal cluster size. 24,[32][33][34][35][36] One such example is the direct production of acetaldehyde from ethanol over Fe-exchanged mordenite (Fe-MOR) zeolites prepared by both solution-state and solid-state ion-exchange methods.…”