Table 2 Best-fit EXAFS parameters for Pd1Cu5-Y.

From: Elucidating the mechanism of heterogeneous Wacker oxidation over Pd-Cu/zeolite Y by transient XAS

 

Scattering pair

Na

R(Ã…)b

σ2(Å2)c

∆E(eV)d

R-factore

Cu K-edge

      

As-prepared

Cu-O

4.5 (0.2)

1.94 (0.004)

0.006 (0.001)

1.0 (0.6)

0.002

Pre-treated (378 K, O2)

Cu-O

4.4 (0.2)

1.94 (0.004)

0.006 (0.001)

3.1 (0.9)

0.004

Wacker-equilibrated (4 hr)

Cu-O

4.2 (0.2)

1.95 (0.004)

0.006 (0.001)

1.3 (0.5)

0.001

Low pO2, 60 min

Cu-O

3.8 (0.1)

1.94 (0.004)

0.007 (0.001)

0.8 (0.6)

0.002

High pO2, 60 min

Cu-O

4.2 (0.1)

1.94 (0.004)

0.007 (0.001)

0.8 (0.5)

0.001

Pd K-edge

      

As-prepared

Pd-O/N

3.6 (0.2)

2.01 (0.01)

0.003 (0.001)

3.1 (1.0)

0.009

Pre-treated (378 K, O2)

Pd-O/N

3.5 (0.2)

2.01 (0.01)

0.004 (0.001)

8.5 (1.3)

0.010

Wacker-equilibrated (4 hr)

Pd-O/N

3.1 (0.3)

2.01 (0.01)

0.004 (0.001)

2.5 (1.5)

0.009

 

Pd-Pd

1.5 (0.9)

2.76 (0.05)

0.018 (0.003)

7.9 (2.5)

 

Low pO2, 60 min

Pd-O/N

2.6 (0.4)

2.01 (0.01)

0.005 (0.003)

2.9 (1.9)

0.014

 

Pd-Pd

1.5 (1.0)

2.78 (0.07)

0.015 (0.009)

2.8 (2.0)

 

High pO2, 60 min

Pd-O/N

2.9 (0.3)

2.01 (0.01)

0.006 (0.003)

3.0 (2.0)

0.047

 

Pd-Pd

1.4 (1.0)

2.78 (0.07)

0.014 (0.010)

3.9 (2.2)

 
  1. EXAFS extended X-ray absorption fine structure, standard errors in brackets.
  2. aNumber of nearest neighbors determined by fixing the amplitude reduction factor (\({\boldsymbol{S}}_0^2\)) values obtained from the fits to Cu (\({\boldsymbol{S}}_0^2\) = 0.82) and Pd (\({\boldsymbol{S}}_0^2\) = 0.86) foil reference spectra.
  3. bInteratomic distance.
  4. cPseudo Debye-Waller factor.
  5. dShift of the energy threshold.
  6. eR-factor: goodness of fit between experimental and theoretical data.
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