Analog input over-voltage protection using Schottky and Zener Diodes. Can it work?
Yes, that would work fine, but you can make this even more simple:







simulate this circuit &ndash; Schematic created using CircuitLab

Zener diodes behave more or less as a "normal" diode when in forward mode so we can use that to clamp negative voltages.

When using a 12V, 400 mW zener diode the maximum current through the zener diode can be 400mW / 12 V = 33 mA. There will then be 12 V across R1, R1 needs to limit the current to 33 mA so it needs to be: 12 V / 33 mA = 364 ohm or higher. I added some margin and suggest 470 ohms then the actual current will be 12 V / 470 ohm = 26 mA and R1 will dissipate 12 * 26 mA = 0.312 W so you might want to use a 0.5 W resistor (or use two 1 kohm 0.25 W resistors in parallel).

I would make the capacitor C1 10 nF, that should suffice to remove most pulses. Only if you need to measure high frequency signals C1 might need to get a smaller value or must be removed. Then the zener diode might be an issue as well as zeners aren't very fast.
But if you stay below 100 kHz or so there should be no issue with this circuit.