You should be exporting as sRGB, please check to make sure you have that set properly in the export dialog box.
yes, i set it sRGB. I wonder if change to 72 dpi that cause grainy?
deepakg1988 - color profile has absolutely nothing to do with this.
To evaluate noise reduction and sharpening, view the image at 100% - any other view will be misleading and incorrect.
In what application are you viewing the exported jpgs?
If the image doesn't fit on screen at 100%, the viewing app resamples the image, and different apps use different resampling algorithms.
Is this the same image exported at the same dimensions, noise reduction, and sharpening from LR and PS?
And ppi has nothing to do with it - it only comes into play when printing.