Edward Chandler You state 'people say that increased dispersion of a metal on a support can lead to scattering away of the x-rays from the oxide lattice faces, leading to a decreased intensity of the support peaks'. Why not ask these people for references?! I find this confusing. In my day (1970's; dinosaurs ruled the earth), I synthesized metallic and bimetallic supported catalysts. Increased metal dispersion (often via lower concentration of precursors) usually led to smaller sizes and thus reduced XRD intensity but broader peaks (Scherrer equation). Supports were generally amorphous (e.g. silica, carbon black) and thus would not give sharp diffraction peaks. At no stage was the x-ray scattering from the support an issue.

Hi Alan F Rawle - Thanks for the response! I have actually asked them for references and have not gotten any. I spent a couple hours looking for something, and didn't find any supporting evidence, so I thought I'd ask on researchgate to see if anyone knew anything.

I'm now wondering if its simply smaller nanoparticles have a higher likelihood of working their way between the basal planes of carbon, and distort the spacing, broadening that peak specifically. This would trend the same way that the hypothesis of the people I've talked to would trend. I suppose a way to test this would be to try the same prep method on an oxide.

Thanks!

Edit: I'm also not sure why I wrote "oxide" in the original answer. We are using carbon black.

Edward Chandler What does the XRD pattern of the support carbon black look like? That is, with no metal loading.

Dear Edward Chandler ,

what is the estimated thickness (mass coverage) of your 'metals' on top of your substrate and how much your substrate peaks decreased?

Any coverage will cause x-ray attenuation and thus will lead to a reduction of the substrate peaks.

The question is, does the strength of coverage match with the observed decrease of peaks in your case...

Best regards

G.M.

Alan F Rawle Its just your standard 002, 100, and 110 graphitic type carbon structure. See attached xrd profile.

Gerhard Martens we have done anything from 0.5wt% (0.06atom/nm2) to 7wt% (just under 1atom/nm2). Yes, the loading itself certainly does trend with a decrease in the support peak in xrd from absorption and scattering. However, it is the change in support peak with changing particle size at constant loading that is our concern here.

Edward Chandler One thought. It's always good to 'follow the particle'. So, what happens to the carbon black? Do you make a conventional supported metal catalyst by impregnating appropriate metal precursors on it, vigorously stirring, reducing, then drying? My thought is during the processing stage you deagglomerate any loose lumps within the carbon black powder and thus reducing the scattering intensity. I wouldn't expect this to be a large effect though. Or, is your metal loading high? Typically I worked with 0.5 % - 5%Metal/Support but at higher loadings we have reduced support content. If you had a 15% loading, for example, then you'd have 0.85 of the original unsupported carbon black loading and thus reduced support intensity.

Dear Edward Chandler，our work （Inorg. Chem. Front., 2020,7, 1298-1306）has reported this phenomenon, where the higher the metal loading, the lower the dispersibility, and the stronger the XRD peak intensity.

Xiugang Li Your report is the expected behavior - higher loading generally leads to larger (metal) sizes, less effective SSA, and contributes to higher metal XRD peak intensity. The poster is talking about decreased support intensity with increased metal dispersion (i.e. higher metal SSA).