A friend of mine has this Dypsis lutescens plant that was almost destroyed by a cat and she wants to know what can be applied on the stems, leaves or on the soil to deter the cat from fighting it anymore. Coffee ground and cigarette ashes might discourage the little monster, but can it also hurt the plant?
Cats don't like the smell of Pelargoniums, so adding a couple of pots of those around the base of the existing plants might help. Otherwise, try mothballs, but you need the old fashioned, napthalene type, that really smell strongly. The drawback with those is, the owner will be able to smell them too. Chili powder is often mentioned, but its not wise to use it - when cats get it on their paws and then clean them, its not a comfortable experience for them.
But, as its an indoor cat, it may only be attacking the plants because it needs to eat some grass - cats chew on grass to act as an emetic, which enables them to get rid of fur balls, which is essential. You can buy grass for cats, often sold as cat grass, in many outlets, and also at Amazon, or seed for growing it, example here.