Achieving controllable distribution of metal cations (Pd, Pt, Ni, Cr, Cu) in a zeolite either as [M(II)-OH]/1Al or M(II)/2Al provides novel mechanistic insights for adsorptive and catalytic reactions

Utilizing H-BEA zeolites with similar Si/Al ratios but with different Al site distributions we show that the divalent metal cations (Ni, Pd, Pt, Cr, Cu) can be dispersed predominantly as either M(II)/2Al species (for conventional zeolite prepared in the hydroxide media) or as [M(II)-OH]/1Al species (for H-BEA prepared in HF). M(II) species are active in ethylene dimerization. However, Pd(II)-OH and Ni(II)-OH species, that were not previously prepared or evaluated for this reaction, are even more catalytically active. M(II)-OH species in zeolite can activate ethylene via formation of C2H4--M(II)-OC2H5 species which can eliminate butene restoring M(II)-OH species. We also reveal that Pt(II) and Pt(II)-OH in zeolite, not previously known to catalyze ethylene dimerization on solid materials, are in fact catalytically active. This synthetic realization further exemplifies the different NO adsorption aspects of these materials. Both Pd(II) and Pd(II)-OH are active for NO adsorption, the latter desorbing NO at higher temperature than isolated Pd(II). Notably, Pd(II)-OH is active for Wacker oxidation chemistry of ethylene into acetaldehyde, whereas Pd(II) is less active: this clarifies the missing mechanistic aspects of Wacker oxidation by homogeneous complexes. The presence of OH ligand in the Pd(II) first coordination sphere is important for reactivity. Further, we show that Cr/2Al in H-BEA is inactive for ethylene oligomerization, whereas Cr-OH has ethylene dimerization activity, illuminating a previously unknown possibility that Cr-OH species could be an active species for Cr/silica Phillips ethylene oligomerization catalysts.