This looks like what is commonly called "leaf scorch." The cause could be any number of things.

I can see the tree is located next to a brick wall and maybe a path leading to the from door. 

Does this area get hit by late afternoon sun? Japanese maples can "burn" from too much heat or sun. Our recent temperature spike could have damaged the leaves (heat bounces off the wall and the path and can exacerbate it). 

Have you recently power-washed the path? Water and chemicals in water could have damaged the tree.

Have you recently fertilized or use an herbicide in the area? Some of it may have drifted onto the leaves. Too much fertilizer can also damage roots and lead to leaf scorch. 

Does this tree get watered regularly? Again, Japanese maples are particularly sensitive to environmental factors. If it is not receiving adequate water, it will be more susceptible to leaf scorch.