I tried it with the PC of a friend of mine and after downloading appeared:"your mac is not supported".
following an explanation from the website www.trustedreviews.com
Despite Apple's guidance that it's only late-2009 devices and onwards that will be able to run the OS, theoretically you should be able to run Sierra on computers with a CPU utilising the Penryn microarchitecture.
Related: How to download macOS Sierra right now
Of course, just because it's possible doesn't mean it's straightforward, which is why developer Colin Mistr (aka dosdude1) created the macOS Sierra Patch Tool.
That utility, along with a USB drive with a capacity of at least 8GB and a copy of Sierra, should let you install macOS on that handful of older devices.
All the usual caveats apply: installing macOS Sierra on an unsupported computer could bork it (and your data), as well as likely voiding your warranty.
On certain devices, too, the workaround will kill your Wi-Fi functionality. These are the late-2008 and mid-2009 MacBook Air, early-2008 and mid-2008 MacBook Pro, early-2008 iMac and early-2008 Mac Pro.
In other words, you should have bit of technical know-how if you're going to try this, and backup all your data first. While we know this worked on Sierra dev previews, we're also unsure if Apple has managed to patch the borderline 'hack', so let us know your mileage in the comments below.
If you do want to give it a go, though, you can find step-by-step instructions and download the macOS Sierra Patch tool here